首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   79897篇
  免费   13015篇
  国内免费   7415篇
化学   69864篇
晶体学   928篇
力学   2823篇
综合类   607篇
数学   6870篇
物理学   19235篇
  2025年   17篇
  2024年   420篇
  2023年   811篇
  2022年   1445篇
  2021年   1831篇
  2020年   3144篇
  2019年   4629篇
  2018年   2320篇
  2017年   1854篇
  2016年   5272篇
  2015年   5265篇
  2014年   5512篇
  2013年   6888篇
  2012年   6284篇
  2011年   5696篇
  2010年   5286篇
  2009年   5213篇
  2008年   5106篇
  2007年   4336篇
  2006年   3890篇
  2005年   3661篇
  2004年   3131篇
  2003年   2790篇
  2002年   3593篇
  2001年   2648篇
  2000年   2348篇
  1999年   1340篇
  1998年   750篇
  1997年   664篇
  1996年   608篇
  1995年   546篇
  1994年   470篇
  1993年   426篇
  1992年   349篇
  1991年   299篇
  1990年   287篇
  1989年   233篇
  1988年   171篇
  1987年   156篇
  1986年   124篇
  1985年   119篇
  1984年   65篇
  1983年   61篇
  1982年   46篇
  1981年   41篇
  1980年   28篇
  1979年   16篇
  1978年   19篇
  1977年   19篇
  1973年   20篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
Colloidal silica suspensions are widely used in many fields, including environmental restoration, oil drilling, and food and medical industries. To control the rheological property of suspensions, poly(ethylene oxide) (PEO) polymers are often used. Under specific conditions, the silica-PEO suspension can create a phenomenon called a shake-gel. Previous works discussed the conditions necessary to form a shake-gel and suggested that the bridging effect of the polymer is one of the important mechanisms for shake-gel formation. However, we noted that the influence of PEO size compared to the separation distance between silica particles regarding shake-gel formation has not been systematically investigated, while the PEO size should be larger than the particle–particle separation distance for polymer bridging in order to form gels. Thus, we conducted a series of experiments to examine the effects of the radius of gyration of the PEO and the distance between the silica particles by controlling the PEO molecular weight and the silica concentration. Our results elucidated that the radius of gyration of the PEO should be 2.5 times larger than the distance between the silica surfaces in order to promote the formation of a shake-gel. This result supports the hypothesis that the bridging effect is the main cause of shake-gel formation, which can help us to understand the conditions necessary for shake-gel preparation.  相似文献   
122.
Heme proteins perform a variety of biological functions and also play significant roles in the field of bio-catalysis. The β-lactamase activity of heme proteins has rarely been reported. Herein, we found, for the first time, that myoglobin (Mb), an O2 carrier, also exhibits novel β-lactamase activity by catalyzing the hydrolysis of ampicillin. The catalytic proficiency ((kcat/KM)/kuncat) was determined to be 6.25 × 1010, which is much higher than the proficiency reported for designed metalloenzymes, although it is lower than that of natural β-lactamases. Moreover, we found that this activity could be regulated by an engineered disulfide bond, such as Cys46-Cys61 in F46C/L61C Mb or by the addition of imidazole to directly coordinate to the heme center. These results indicate that the heme active site is responsible for the β-lactamase activity of Mb. Therefore, the study suggests the potential of heme proteins acting as β-lactamases, which broadens the diversity of their catalytic functions.  相似文献   
123.
Cardiovascular disease caused by atherosclerosis (AS) seriously affects human health. Photothermal therapy (PTT) brings hope to the diagnosis and treatment of AS, with the development of nanotechnology. To improve treatment efficiency, self-assembled CuCo2S4 nanocrystals (NCs) were developed as a drug-delivery nanocarrier, triggered by near-infrared (NIR) light for efficient chemophotothermal therapy of arterial inflammation. The as-prepared self-assembled CuCo2S4 NCs exhibited excellent biocompatibility and a very high chloroquine (CL)-loading content. In addition, the self-assembled CuCo2S4 NCs/CL nanocomposites showed good photothermal performance, due to strong absorption in the NIR region, and the release of CL from the NCs/CL nanocomposites was driven by NIR light. When illuminated by NIR light, both PTT from the NCs and chemotherapy from the CL were simultaneously triggered, resulting in killing macrophages with a synergistic effect. Moreover, chemo-photothermal therapy with CuCo2S4 NCs/CL nanocomposites showed an effective therapeutic effect for arterial inflammation, in vivo. Our work demonstrated that chemo-photothermal therapy could be a promising strategy for the treatment of arterial inflammation against atherosclerosis.  相似文献   
124.
Baijiu is a unique and traditional distilled liquor in China. Flavor plays a crucial rule in baijiu. Up to now, the research on the flavor of baijiu has progressed from the identification of volatile compounds to the research on key aroma compounds, but the release mechanism of these characteristic compounds is still unclear. Meanwhile, volatile compounds account for only a tiny fraction, whereas ethanol and water account for more than 98% of the content in baijiu. By summarizing the ethanol–water hydrogen bond structure in different alcoholic beverages, it was found that flavor compounds can affect the association strength of the ethanol–water hydrogen bond, and ethanol–water can also affect the interface distribution of flavor compounds. Therefore, the research on ethanol–water microstructure in baijiu is helpful to realize the simple visualization of adulteration detection, aging determination and flavor release mechanism analysis of baijiu, and further uncover the mystery of baijiu.  相似文献   
125.
When Aristolochia plants wilt and decay, aristolochic acids (AAs) are released into the soil, causing soil contamination. It has been demonstrated that aristolochic acid can be accumulated and enriched in crops through plant uptake. However, there is a lack of systematic studies on the migration and accumulation of AAs in a realistic simulated soil environment. In this study, Aristolochia herbal extracts were mixed with soil for growing three typical vegetables: lettuce, celery, and tomato. The contents of AAs in the above-mentioned plants were determined by an established highly sensitive LC-MS/MS method to study the migration and accumulation of AAs. We found that AAs in the soil can be transferred and accumulated in plants. AAs first entered the roots, which were more likely to accumulate AAs, and partially entered the above-ground parts. This further confirms that AAs can enter the food chain through plants and can have serious effects on human health. It was also shown that plants with vigorous growth and a large size absorbed AAs from the soil at a faster rate. The more AAs present in the soil, the more they accumulated in the plant.  相似文献   
126.
Determining the different surfaces of oxide nanocrystals is key in developing structure–property relations. In many cases, only surface geometry is considered while ignoring the influence of surroundings, such as ubiquitous water on the surface. Here we apply 17O solid-state NMR spectroscopy to explore the facet differences of morphology-controlled ceria nanocrystals considering both geometry and water adsorption. Tri-coordinated oxygen ions at the 1st layer of ceria (111), (110), and (100) facets exhibit distinct 17O NMR shifts at dry surfaces while these 17O NMR parameters vary in the presence of water, indicating its non-negligible effects on the oxide surface. Thus, the interaction between water and oxide surfaces and its impact on the chemical environment should be considered in future studies, and solid-state NMR spectroscopy is a sensitive approach for obtaining such information. The work provides new insights into elucidating the surface chemistry of oxide nanomaterials.

Both atomic geometry and the influence of surroundings (e.g., exogenously coordinated water) are key issues for determining the chemical environment of oxide surfaces, whereas the latter is usually ignored and should be considered in future studies.  相似文献   
127.
The search for new zeolite structures and compositions remains important in synthetic materials science due to the high impact on developing new chemical technologies, as well as on improving existing ones. Herein we present the synthesis and structure of PST-35, a novel medium-pore germanosilicate (Si/Ge = 2.1–6.6) zeolite, achieved by combining the excess fluoride approach and the unique structure directing ability of Ge in the presence of 1,2,3-triethylimidazolium ions as an organic structure-directing agent. PST-35 contains a zig-zag 10-ring (4.6 × 6.7 Å) channel system constructed of strictly alternating large 28-hedral ([48·58·68·82·102]) and smaller 18-hedral ([46·54·64·82·102]) cages of anomalous orthorhombic shape. The PST-35 structure is built from the connection of pst-35 layers consisting of small 8-hedral ([43·54·6]) cages, previously unobserved zeolite building layers, through single 4-rings.

A medium-pore zeolite containing 2 novel orthorhombic-shaped cages was synthesized by combining the tendency of Ge to form double 4-ring units with the structure-directing ability of 1,2,3-triethylimidazolium ions under excess fluoride conditions.  相似文献   
128.
Phototherapy has been a promising therapeutic modality for pathological tissue due to its spatiotemporal selectivity and non-invasive characteristics. However, as a core component of phototherapy, a single photosensitizer (PS) nanoplatform integrating excellent therapeutic efficiency and minimal side effects remains an urgent but unmet need. Here, we construct a J-aggregated nano-porphyrin termed MTE based on the self-assembly of methyl-pheophorbide a derivative MPa-TEG (MT) and natural polyphenolic compound epigallocatechin gallate (EGCG). Due to the synergistic interaction between similar large π-conjugated structural EGCG and MT, MTE with small and uniform size is obtained by effectively hindering Ostwald ripening of MT. Noteworthily, MTE not only effectively avoids the inadvertent side effects of phototoxicity during transport thank to the ability of reactive oxygen species (ROS) scavenging, but also achieves two-pathway augmented superior phototherapy: (1) enhancing photodynamic therapy (PDT) via inhibiting the expression of anti-apoptosis protein surviving; (2) achieving adjuvant mild-temperature laser interstitial thermal therapy (LITT) via reducing the tumor thermoresistance on account that MTE inhibits the overexpression of HSP 70 and HSP 90. This research not only offers a facile strategy to construct multicomponent nanoplatforms but also provides a new pathway for efficient and low-toxicity phototherapy, which is beneficial to the future clinical application.

J-aggregated nanoporphyrin (MTE) integrates minimal side effects and two-pathway augmented superior phototherapy: enhancing photodynamic therapy (PDT) and achieving adjuvant mild-temperature laser interstitial thermal therapy (LITT).  相似文献   
129.
Reversibility and stability are considered as the key indicators for Zn metal anodes in aqueous Zn-ion batteries, yet they are severely hindered by uncontrolled Zn stripping/plating and side reactions. Herein, we fabricate a bulk phase ZnIn alloy anode containing trace indium by a typical smelting–rolling process. A uniformly dispersed bulk phase of the whole Zn anode is constructed rather than only a protective layer on the surface. The Zn deposition can be regarded as instantaneous nucleation due to the adsorption of the evenly dispersed indium, and formation of the exclusion zone for further nucleation can be prevented at the same time. Owing to the bulk phase structure of ZnIn alloy, the indium not only plays a crucial role in Zn deposition, but also improves the Zn stripping. Consequently, the as-designed ZnIn alloy anode can sustain stable Zn stripping/plating for over 2500 h at 4.4 mA cm−2 with nearly 6 times smaller voltage hysteresis than that of pure Zn. Moreover, it enables a substantially stable ZnIn//NH4V4O10 battery with 96.44% capacity retention after 1000 cycles at 5 A g−1. This method of regulating the Zn nucleation by preparing a Zn-based alloy provides a potential solution to the critical problem of Zn dendrite growth and by-product generation fundamentally.

A ZnIn alloy anode with trace indium is obtained by smelting–rolling method. The Zn deposition could be regarded as instantaneous nucleation that can alleviate the effect of deposition layer for the diffusion zone and suppresses dendrite growth.  相似文献   
130.
Inducing the surface enrichment of active noble metal can not only help to stabilize the catalyst but also modify the catalytic performance of the catalyst through electronic and geometric effects. Herein, we report the in situ surface enrichment of Ir on IrRu alloy during the oxygen evolution reaction (OER). The surface enrichment of Ir was probed by ex situ high-resolution transmission electron microscopy (HRTEM), in situ X-ray absorption spectroscopy (XAS), and electrochemical Cu stripping, leading to complementary characterizations of the dynamic reconstruction of the IrRu alloy during OER. Guided by the density functional theory (DFT), an IrRu alloy with low Ir content (20 wt%) was constructed, which displayed a low overpotential of only 230 mV to deliver an OER current density of 10 mA cm−2 in 0.1 M HClO4 solution and maintained stable performance for over 20 h. To investigate the practical application potential, a proton exchange membrane (PEM) water electrolyzer using the IrRu alloy as the anode catalyst was assembled, which required a low cell voltage of only 1.48 V to generate a current density of 1 A cm−2.

Inducing the surface enrichment of active noble metal can not only help to stabilize the catalyst but also modify the catalytic performance of the catalyst through electronic and geometric effects.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号