全文获取类型
收费全文 | 27169篇 |
免费 | 4504篇 |
国内免费 | 4048篇 |
专业分类
化学 | 20719篇 |
晶体学 | 432篇 |
力学 | 1407篇 |
综合类 | 297篇 |
数学 | 3019篇 |
物理学 | 9847篇 |
出版年
2024年 | 233篇 |
2023年 | 529篇 |
2022年 | 976篇 |
2021年 | 1046篇 |
2020年 | 1090篇 |
2019年 | 1149篇 |
2018年 | 972篇 |
2017年 | 1004篇 |
2016年 | 1300篇 |
2015年 | 1351篇 |
2014年 | 1688篇 |
2013年 | 2089篇 |
2012年 | 2485篇 |
2011年 | 2544篇 |
2010年 | 1946篇 |
2009年 | 1842篇 |
2008年 | 1954篇 |
2007年 | 1806篇 |
2006年 | 1687篇 |
2005年 | 1353篇 |
2004年 | 998篇 |
2003年 | 787篇 |
2002年 | 741篇 |
2001年 | 655篇 |
2000年 | 574篇 |
1999年 | 482篇 |
1998年 | 355篇 |
1997年 | 313篇 |
1996年 | 270篇 |
1995年 | 254篇 |
1994年 | 233篇 |
1993年 | 168篇 |
1992年 | 146篇 |
1991年 | 135篇 |
1990年 | 121篇 |
1989年 | 90篇 |
1988年 | 76篇 |
1987年 | 57篇 |
1986年 | 64篇 |
1985年 | 52篇 |
1984年 | 21篇 |
1983年 | 18篇 |
1982年 | 19篇 |
1981年 | 6篇 |
1980年 | 8篇 |
1979年 | 8篇 |
1978年 | 4篇 |
1971年 | 4篇 |
1957年 | 4篇 |
1936年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
81.
Xueyan Lu Yan Jin Xiaorui Guo Mingyuan Xu Zhonghua Tang Qi Chen 《Molecules (Basel, Switzerland)》2022,27(24)
Coexisting salt and alkaline stresses seriously threaten plant survival. Most studies have focused on halophytes; however, knowledge on how plants defend against saline–alkali stress is limited. This study investigated the role of Taraxacum mongolicum in a Puccinellia tenuiflora community under environmental saline–alkali stress to analyse the response of elements and metabolites in T. mongolicum, using P. tenuiflora as a control. The results show that the macroelements Ca and Mg are significantly accumulated in the aboveground parts (particularly in the stem) of T. mongolicum. Microelements B and Mo are also accumulated in T. mongolicum. Microelement B can adjust the transformation of sugars, and Mo contributes to the improvement in nitrogen metabolism. Furthermore, the metabolomic results demonstrate that T. mongolicum leads to decreased sugar accumulation and increased amounts of amino acids and organic acids to help plants resist saline–alkali stress. The resource allocation of carbon (sugar) and nitrogen (amino acids) results in the accumulation of only a few phenolic metabolites (i.e., petunidin, chlorogenic acid, and quercetin-3-O-rhamnoside) in T. mongolicum. These phenolic metabolites help to scavenge excess reactive oxygen species. Our study primarily helps in understanding the contribution of T. mongolicum in P. tenuiflora communities on coping with saline–alkali stress. 相似文献
82.
Yiwen Zhang Kunjian Liu Chengqiu Yan Yu Yin Shuangyan He Li Qiu Guofeng Li 《Molecules (Basel, Switzerland)》2022,27(24)
Colorectal cancer (CRC) is a prevalent and serious gastrointestinal malignancy with high mortality and morbidity. Chemoprevention refers to a newly emerged strategy that uses drugs with chemopreventive properties to promote antioxidation, regulate cancer cell cycle, suppress proliferation, and induce cellular apoptosis, so as to improve cancer treatment outcomes. Natural polyphenols are currently recognized as a class of chemopreventive agents that have shown remarkable anticarcinogenic properties. Numerous in vitro and in vivo studies have elucidated the anti-CRC mechanisms of natural polyphenols, such as regulation of various molecular and signaling pathways. Natural polyphenols are also reportedly capable of modulating the gut microbiota and cancer stem cells (CSCs) to suppress tumor formation and progression. Combined use of different natural polyphenols is recommended due to their low bioavailability and instability, and combination treatment can exert synergistical effects, reduce side effects, and avoid drug resistance in CRC treatment. In summary, the application of polyphenols in the chemoprevention and treatment of CRC is promising. Further clinical evaluation of their effectiveness is warranted and anticipated. 相似文献
83.
Chao Wang Xiaoxue Zhao Dabing Li Dr. Chong Yan Qiang Zhang Li-Zhen Fan 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2024,136(19):e202317856
In solid-state lithium metal batteries (SSLMBs), the inhomogeneous electrolyte-electrode interphase layer aggravates the interfacial stability, leading to discontinuous interfacial ion/charge transport and continuous degradation of the electrolyte. Herein, we constructed an anion-modulated ionic conductor (AMIC) that enables in situ construction of electrolyte/electrode interphases for high-voltage SSLMBs by exploiting conformational transitions under multiple interactions between polymer and lithium salt anions. Anions modulate the decomposition behavior of supramolecular poly (vinylene carbonate) (PVC) at the electrode interface by changing the spatial conformation of the polymer chains, which further enhances ion transport and stabilizes the interfacial morphology. In addition, the AMIC weakens the “Li+-solvation” and increases Li+ vehicle sites, thereby enhancing the lithium-ion transport number (tLi+=~0.67). Consequently, Li || LiNi0.8Co0.1Mn0.1O2 cell maintains about 85 % capacity retention and Coulombic efficiency >99.8 % in 200 cycles at a charge cut-off voltage of 4.5 V. This study provides a new understanding of lithium salt anions regulating polymer chain segment behavior in the solid-state polymer electrolyte (SPE) and highlights the importance of the ion environment in the construction of interfacial phases and ionic conduction. 相似文献
84.
85.
Qianqian Shen Juzhang Yan Yuchen Han Prof. Dr. Zaoxiao Zhang Huanhuan Li Prof. Dr. Dulin Kong Prof. Dr. Jianjun Shi Prof. Dr. Chengsen Cui Prof. Dr. Wuyuan Zhang 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2024,136(21):e202401590
Enantiomerically pure organoperoxides serve as valuable precursors in organic transformations. Herein, we present the first examples of unspecific peroxygenase catalyzed kinetic resolution of racemic organoperoxides through asymmetric reduction. Through meticulous investigation of the reaction conditions, it is shown that the unspecific peroxygenase from Agrocybe aegerita (AaeUPO) exhibits robust catalytic activity in the kinetic resolution reactions of the model substrate with turnover numbers up to 60000 and turnover frequency of 5.6 s−1. Various aralkyl organoperoxides were successfully resolved by AaeUPO, achieving excellent enantioselectivities (e.g., up to 99 % ee for the (S)-organoperoxide products). Additionally, we screened commercial peroxygenase variants to obtain the organoperoxides with complementary chirality, with one mutant yielding the (R)-products. While unspecific peroxygenases have been extensively demonstrated as a powerful oxidative catalysts, this study highlights their usefulness in catalyzing the reduction of organoperoxides and providing versatile chiral synthons. 相似文献
86.
产业运行的市场治理主要是指交易过程中以契约、成本和价格等为核心的市场调节,属于基础经济理论层级上的治理结构;当市场治理面临竞争和垄断时,它在一定程度上也包括政府产业规制;当我们将流通领域作为一个独立产业部门对待时,政府较少对流通产业进行规制以及流通产业竞争充分的事实,使大部分经济学家倾向于认为流通产业的市场治理可以不包括政府产业规制。据此,需要研究的问题是:流通产业的市场治理通常呈现何种格局,与第一和第二产业比较,流通产业市场治理结构在什么样的条件下发生变动,这些变动要不要包括政府产业规制,这些变动以什么样的形式与竞争和垄断相联系,等等。因此,有必要研究和探讨流通产业市场治理的特定图景,流通领域的契约类型、契约联结方式以及契约执行等市场性制度安排,政府产业规制和厂商行为对市场治理结构变动的影响,流通产业市场治理及其结构变动究竟需不需要政府产业规制等问题。在此基础上,可望对流通产业市场治理结构展开一般性描述。 相似文献
87.
88.
Wang Xiaojing Han Wenxiu Yan Xin Zhang Jun Yang Mengqi Jiang Pei 《Molecular diversity》2020,24(2):407-412
Molecular Diversity - Methods of three-dimensional molecular alignment generally treat all pharmacophore features equally when superimposing. However, some pharmacophore features can be more... 相似文献
89.
由于银纳米粒子结构的表面等离激元共振特性对有机无机卤化物钙钛矿的新型太阳能电池性能有一定影响,利用comsol mutiphysics多物理场仿真软件对Ag@CH3 NH3 PbI3纳米粒子等离激元效应增强钙钛矿太阳能薄膜电池性能进行研究,对粒子半径和粒子间距对于能量的影响进行了计算;对光敏层能量增强的机理进行了解释;并对电场分布进行了详细说明.依据实验数据,给出优化后的银纳米粒子阵列和钙钛矿光敏层的厚度以及强度,为实验制备高效稳定的钙钛矿太阳能电池提供理论指导. 相似文献
90.
Birui Shi Yan Zhang Baolin Huang Huiping Lin Qiong Zhou Yujue Wang Zheng Cai Menghua Liu 《Molecules (Basel, Switzerland)》2022,27(3)
With the widespread clinical use of drug combinations, the incidence of drug–drug interactions (DDI) has significantly increased, accompanied by a variety of adverse reactions. Drug transporters play an important role in the development of DDI by affecting the elimination process of drugs in vivo, especially in the pathological state. Tubulointerstitial fibrosis (TIF) is an inevitable pathway in the progression of chronic kidney disease (CKD) to end-stage renal disease. Here, the dynamic expression changes of eleven drug transporters in TIF kidney have been systematically investigated. Among them, the mRNA expressions of Oat1, Oat2, Oct1, Oct2, Oatp4C1 and Mate1 were down-regulated, while Oat3, Mrp2, Mrp4, Mdr1-α, Bcrp were up-regulated. Pearson correlation analysis was used to analyze the correlation between transporters and Creatinine (Cr), OCT2 and MATE1 showed a strong negative correlation with Cr. In contrast, Mdr1-α exhibited a strong positive correlation with Cr. In addition, the pharmacokinetics of cimetidine, ganciclovir, and digoxin, which were the classical substrates for OCT2, MATE1 and P-glycoprotein (P-gp), respectively, have been studied. These results reveal that changes in serum creatinine can indicate changes in drug transporters in the kidney, and thus affect the pharmacokinetics of its substrates, providing useful information for clinical use. 相似文献