全文获取类型
收费全文 | 168495篇 |
免费 | 35660篇 |
国内免费 | 27108篇 |
专业分类
化学 | 112135篇 |
晶体学 | 2073篇 |
力学 | 11368篇 |
综合类 | 918篇 |
数学 | 21252篇 |
物理学 | 83517篇 |
出版年
2024年 | 572篇 |
2023年 | 2418篇 |
2022年 | 3396篇 |
2021年 | 3780篇 |
2020年 | 4337篇 |
2019年 | 4723篇 |
2018年 | 4342篇 |
2017年 | 4726篇 |
2016年 | 6141篇 |
2015年 | 6592篇 |
2014年 | 7344篇 |
2013年 | 10664篇 |
2012年 | 12287篇 |
2011年 | 14102篇 |
2010年 | 14864篇 |
2009年 | 15067篇 |
2008年 | 9504篇 |
2007年 | 8320篇 |
2006年 | 7653篇 |
2005年 | 7150篇 |
2004年 | 6974篇 |
2003年 | 5571篇 |
2002年 | 5231篇 |
2001年 | 5235篇 |
2000年 | 4213篇 |
1999年 | 4432篇 |
1998年 | 3674篇 |
1997年 | 3314篇 |
1996年 | 3664篇 |
1995年 | 3857篇 |
1994年 | 3877篇 |
1993年 | 3727篇 |
1992年 | 3219篇 |
1991年 | 2777篇 |
1990年 | 2341篇 |
1989年 | 2340篇 |
1988年 | 2213篇 |
1987年 | 1495篇 |
1986年 | 1493篇 |
1985年 | 1167篇 |
1984年 | 1174篇 |
1983年 | 543篇 |
1982年 | 1028篇 |
1981年 | 849篇 |
1980年 | 854篇 |
1979年 | 591篇 |
1978年 | 593篇 |
1977年 | 696篇 |
1976年 | 1096篇 |
1972年 | 563篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
Ping Chen Yanhong Hao Xinxin Wang Prof. Dr. Dan Yuan Prof. Dr. Yingming Yao Prof. Dr. Lutz Ackermann 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(30):7292-7297
Highly position selective alkylations of N-alkylindoles at C7-positions have been enabled by cationic zirconium complexes. The strategy provides a straightforward access to install alkyl groups at C7-positions of indoles without a complex directing group. Mechanistic studies provided support for the importance of Brønsted acids in the catalytic manifold. 相似文献
122.
Lan-Lan Zhang Dr. Wen-Ke Miao Dr. Li-Jun Ren Yu-Kun Yan Dr. Yue Lin Prof. Wei Wang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(58):13396-13401
Organic polymers and inorganic clusters belong to two different disciplines and have completely different properties and structures. When a cluster is attached to the backbone of a polymer as a pendant, the resultant hybrid polymers (polyclusters) exhibit unique behaviours totally different from those of conventional polymers owing to the nanoscale size of the cluster and its particular interactions. Herein, the aggregation of a poly(polyoxometalate)—a polynorbornene backbone with inorganic polyoxometalate cluster pendants—upon addition of a non-solvent to its dilute solution is reported. A three-dimensional network of tangled and snake-like nanothreads was observed. Direct visualisation of individual nanoscale clusters enabled identification of single chains within the nanothreads. These observations suggest that during the process of aggregation, the hybrid polymer forms curved or extended chains as a consequence of an armouring effect in which the collapsed cluster pendants wrap around the backbone. The collapse occurs because they become less soluble in the solvent/non-solvent mixture. The extended chains then become entwined and form nanoropes consisting of multiple chains wound around each other. This study provides a deeper understanding of the nature of polyclusters and should also prove useful for their future development and application. 相似文献
123.
Rongzhen Wu Hongyu Chen Dr. Ninghui Chang Yuzhi Xu Prof. Dr. Jiao Jiao Prof. Dr. Hailong Zhang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(6):1166-1195
Bryostatins are a class of naturally occurring macrocyclic lactones with a unique fast developing portfolio of clinical applications, including treatment of AIDS, Alzheimer's disease, and cancer. This comprehensive account summarizes the recent progress (2014–present) in the development of bryostatins, including their total synthesis and biomedical applications. An emphasis is placed on the discussion of bryostatin 1 , the most-studied analogue to date. This review highlights the synthetic and biological challenges of bryostatins and provides an outlook on their future development. 相似文献
124.
Here, we report a new strategy for rapid synthesis of branched peptide by side-chain hydrazide ligation at Asn. The hydrazide was converted to thioester at Asn side chain by NaNO2 and thiol reagent, and sequential ligation with an N-terminus Cys-peptide efficiently afforded the branched peptide. A branched cyclic peptide was successfully synthesized by side-chain ligation with a two-Cys-peptide and formation of a disulfide bond. This approach provides a new way for expeditious synthesis of branched peptides and facilitates the design of neopeptides as functional bio-mimics. 相似文献
125.
Nonlinear Dynamics - Nonlinear vibration isolation provides with an effective way for vibration reduction with broad band and high efficiency. This investigation focuses on the dynamic effects of a... 相似文献
126.
Guangrui Chen Yuxing Yan Dr. Jie Wang Prof. Yong Sik Ok Guiyuan Zhong Prof. Bu Yuan Guan Prof. Yusuke Yamauchi 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(44):19831-19836
Mesoporous core–shell nanostructures with controllable ultra-large open channels in their nanoshells are of great interest. However, soft template-directed cooperative assembly to mesoporous nanoshells with highly accessible pores larger than 30 nm, or even above 50 nm into macroporous range, remains a significant challenge. Herein we report a general approach for precisely tailored coating of hierarchically macro-/mesoporous polymer and carbon shells, possessing highly accessible radial channels with extremely wide pore size distribution from ca. 10 nm to ca. 200 nm, on diverse functional materials. This strategy creates opportunities to tailor the interfacial assembly of irregular mesostructured nanounits on core materials and generate various core–shell nanomaterials with controllable pore architectures. The obtained Fe,N-doped macro-/mesoporous carbon nanoshells show enhanced electrochemical performance for the oxygen reduction reaction in alkaline condition. 相似文献
127.
A 1.5-μm eye-safe, 3-D scanning, and compact Mie LIght Detection and Ranging (LIDAR) is presented. The transmitter of the LIDAR is based on a KTA optical parameter oscillator (OPO) resonator. For detecting return signals, an InGaAs APD is used. The all solid-state OPO laser transmitter has the feature of small volume and lightweight, which allows a 165-lb compact eye-safe scanning LIDAR to be constructed. A system simulation using our own model was conducted to direct the system development. A method to solve the problem with small active area APD detectors was developed and described. The preliminary field-test measurement results indicated that the LIDAR has the capability to detect aerosols and clouds in lower atmospheres up to three dimensions. 相似文献
128.
The sunset diagram of λφ4 theory is evaluated numerically in cutoff scheme and a nonzero finite term(in accordance with dimensional regularization (DR) result) is found in contrast to published calculations. This findingdramatically reduces the critical couplings for symmetry breaking in the two-loop effective potential discussed in ourprevious work. 相似文献
129.
Summary Carbon deposits on the surface ofRu/Fe2O3 catalysts used in the water-gas shift reaction have been investigated by Auger Electron Spectrometry. A correlation has been
found between the thickness of the carbon deposit and the catalytic activity in WGSR. The carbon deposit covers the metallic
active centers and blocks their contact with reagents. The dotting of the iron oxide support with sodium has been found to
reduce the amount of carbon deposit. . 相似文献
130.
The γcmc values of CTAB-SDS decrease from 63.67 mN/m at 10‡C to 36.38 mN/m at 90‡C, slightly lower than those of either CTAB or SDS.
Correspondingly, the CMC of CTAB-SDS decreases almost by half. The increase of surface activity of CTAB-SDS can be attributed
to the relatively weak electrostatic interaction at high temperature, which is supported by the increase of solubility of
CTAB-SDS with rise in temperature. Catalytic effect on oxidation of toluene derivatives with potassium permanganate follows
the order CTAB-SDS > SDS > CTAB. This is not caused by the dissociative effect of CTAB-SDS with low surface activity at low
temperature, as seen from the fact that almost all oxidative products can be retrieved for different toluene derivatives and
surfactants by mimicking the conditions of reaction. In the emulsifications of toluene derivatives at 90‡C, the time that
turbid water layers of surfactant solutions take to become clear is the same as that of the catalytic effect on oxidation
of toluene derivatives. Thus, it can be inferred that surfactants can improve the oxidation yields of toluene derivatives
by increasing the contact between two reacting phases. 相似文献