全文获取类型
收费全文 | 30022篇 |
免费 | 1258篇 |
国内免费 | 170篇 |
专业分类
化学 | 21413篇 |
晶体学 | 223篇 |
力学 | 667篇 |
综合类 | 1篇 |
数学 | 4764篇 |
物理学 | 4382篇 |
出版年
2023年 | 172篇 |
2021年 | 345篇 |
2020年 | 578篇 |
2019年 | 589篇 |
2018年 | 326篇 |
2017年 | 341篇 |
2016年 | 839篇 |
2015年 | 827篇 |
2014年 | 929篇 |
2013年 | 1572篇 |
2012年 | 1875篇 |
2011年 | 2173篇 |
2010年 | 1180篇 |
2009年 | 1010篇 |
2008年 | 1731篇 |
2007年 | 1778篇 |
2006年 | 1703篇 |
2005年 | 1658篇 |
2004年 | 1352篇 |
2003年 | 1109篇 |
2002年 | 865篇 |
2001年 | 301篇 |
2000年 | 260篇 |
1999年 | 225篇 |
1998年 | 236篇 |
1997年 | 329篇 |
1996年 | 347篇 |
1995年 | 301篇 |
1994年 | 281篇 |
1993年 | 326篇 |
1992年 | 260篇 |
1991年 | 240篇 |
1990年 | 206篇 |
1989年 | 202篇 |
1988年 | 180篇 |
1987年 | 195篇 |
1986年 | 171篇 |
1985年 | 259篇 |
1984年 | 297篇 |
1983年 | 225篇 |
1982年 | 269篇 |
1981年 | 299篇 |
1980年 | 221篇 |
1979年 | 230篇 |
1978年 | 257篇 |
1977年 | 207篇 |
1976年 | 205篇 |
1975年 | 189篇 |
1974年 | 189篇 |
1973年 | 176篇 |
排序方式: 共有10000条查询结果,搜索用时 171 毫秒
1.
Etémé Armand Sylvin Tabi Conrad Bertand Beyala Ateba Jean Félix Ekobena Fouda Henry Paul Mohamadou Alidou Crépin Kofané Timoléon 《Nonlinear dynamics》2021,105(1):785-795
Nonlinear Dynamics - The fluctuation of ions concentration across the cell membrane of neuron can generate a time varying electromagnetic field. Thus, memristors are used to realize the coupling... 相似文献
2.
3.
Johannes C. B. Dietschreit Annika Wagner T. Anh Le Philipp Klein Prof. Dr. Hermann Schindelin Prof. Dr. Till Opatz Prof. Dr. Bernd Engels Prof. Dr. Ute A. Hellmich Prof. Dr. Christian Ochsenfeld 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(31):12769-12773
The absence of fluorine from most biomolecules renders it an excellent probe for NMR spectroscopy to monitor inhibitor–protein interactions. However, predicting the binding mode of a fluorinated ligand from a chemical shift (or vice versa) has been challenging due to the high electron density of the fluorine atom. Nonetheless, reliable 19F chemical-shift predictions to deduce ligand-binding modes hold great potential for in silico drug design. Herein, we present a systematic QM/MM study to predict the 19F NMR chemical shifts of a covalently bound fluorinated inhibitor to the essential oxidoreductase tryparedoxin (Tpx) from African trypanosomes, the causative agent of African sleeping sickness. We include many protein–inhibitor conformations as well as monomeric and dimeric inhibitor–protein complexes, thus rendering it the largest computational study on chemical shifts of 19F nuclei in a biological context to date. Our predicted shifts agree well with those obtained experimentally and pave the way for future work in this area. 相似文献
4.
5.
AbstractWe study the inverse problem of parameter identification in noncoercive variational problems that commonly appear in applied models. We examine the differentiability of the set-valued parameter-to-solution map using the first-order and the second-order contingent derivatives. We explore the inverse problem using the output least-squares and the modified output least-squares objectives. By regularizing the noncoercive variational problem, we obtain a single-valued regularized parameter-to-solution map and investigate its smoothness and boundedness. We also consider optimization problems using the output least-squares and the modified output least-squares objectives for the regularized variational problem. We give a complete convergence analysis showing that for the output least-squares and the modified output least-squares, the regularized minimization problems approximate the original optimization problems suitably. We also provide the first-order and the second-order adjoint method for the computation of the first-order and the second-order derivatives of the output least-squares objective. We provide discrete formulas for the gradient and the Hessian calculation and present numerical results. 相似文献
6.
Cellulose catalyzed oxidative hydroxylation of aryl and hetero-arylboronic acids to the corresponding phenols under metal and base free strategy has been demonstrated. The sustainable ipso-hydroxylation takes place using hydrogen peroxide as an oxidant in water under mild condition in shorter period of time. Interestingly, easy recovery and reusability of heterogeneous catalyst without significant loss in catalytic yield makes the protocol environmentally benign. 相似文献
7.
Mathematical Programming - A framework is proposed for solving general convex quadratic programs (CQPs) from an infeasible starting point by invoking an existing feasible-start algorithm tailored... 相似文献
8.
Prof. James S. M. Anderson Prof. Juan I. Rodríguez Prof. Paul W. Ayers Daniel E. Trujillo-González Dr. Andreas W. Götz Prof. Jochen Autschbach Prof. Fray L. Castillo-Alvarado Prof. Koichi Yamashita 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(10):2538-2544
The topology of the molecular electron density of benzene dithiol gold cluster complex Au4−S−C6H4−S′−Au′4 changed when relativistic corrections were made and the structure was close to a minimum of the Born–Oppenheimer energy surface. Specifically, new bond paths between hydrogen atoms on the benzene ring and gold atoms appeared, indicating that there is a favorable interaction between these atoms at the relativistic level. This is consistent with the observation that gold becomes a better electron acceptor when relativistic corrections are applied. In addition to relativistic effects, here, we establish the sensitivity of molecular topology to basis sets and convergence thresholds for geometry optimization. 相似文献
9.
Dr. Lukas Kaltschnee Dr. Anil P. Jagtap Dr. Jeffrey McCormick Dr. Shawn Wagner Prof. Dr. Louis-S. Bouchard Prof. Dr. Marcel Utz Prof. Dr. Christian Griesinger Dr. Stefan Glöggler 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(47):11031-11035
NMR offers many possibilities in chemical analysis, structural investigations, and medical diagnostics. Although it is broadly used, one of NMR spectroscopies main drawbacks is low sensitivity. Hyperpolarization techniques enhance NMR signals by more than four orders of magnitude allowing the design of new contrast agents. Parahydrogen induced polarization that utilizes the para-hydrogen's singlet state to create enhanced signals is of particular interest since it allows to produce molecular imaging agents within seconds. Herein, we present a strategy for signal enhancement of the carbonyl 13C in amino acids by using parahydrogen, as demonstrated for glycine and alanine. Importantly, the hyperpolarization step is carried out in water and chemically unmodified canonical amino acids are obtained. Our approach thus offers a high degree of biocompatibility, which is crucial for further application. The rapid sample hyperpolarization (within seconds) may enable the continuous production of biologically useful probes, such as metabolic contrast agents or probes for structural biology. 相似文献
10.
Paul M. Bogie Lauren R. Holloway Courtney Ngai Tabitha F. Miller Divine K. Grewal Prof. Richard J. Hooley 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(43):10232-10238
A self-assembled Fe4L6 cage complex internally decorated with acid functions is capable of accelerating the thioetherification of activated alcohols, ethers and amines by up to 1000-fold. No product inhibition is seen, and effective supramolecular catalysis can occur with as little as 5 % cage. The substrates are bound in the host with up to micromolar affinities, whereas the products show binding that is an order of magnitude weaker. Most importantly, the cage host alters the molecularity of the reaction: whereas the reaction catalyzed by simple acids is a unimolecular, SN1-type substitution process, the rate of the host-mediated process is dependent on the concentration of nucleophile. The molecularity of the cage-catalyzed reaction is substrate-dependent, and can be up to bimolecular. In addition, the catalysis can be prevented by a large excess of nucleophile, where substrate inhibition dominates, and the use of tritylated anilines as substrates causes a negative feedback loop, whereby the liberated product destroys the catalyst and stops the reaction. 相似文献