全文获取类型
收费全文 | 21768篇 |
免费 | 4041篇 |
国内免费 | 3211篇 |
专业分类
化学 | 15773篇 |
晶体学 | 299篇 |
力学 | 1338篇 |
综合类 | 303篇 |
数学 | 2591篇 |
物理学 | 8716篇 |
出版年
2024年 | 55篇 |
2023年 | 386篇 |
2022年 | 750篇 |
2021年 | 800篇 |
2020年 | 911篇 |
2019年 | 895篇 |
2018年 | 768篇 |
2017年 | 730篇 |
2016年 | 1016篇 |
2015年 | 1095篇 |
2014年 | 1330篇 |
2013年 | 1637篇 |
2012年 | 1971篇 |
2011年 | 2062篇 |
2010年 | 1485篇 |
2009年 | 1502篇 |
2008年 | 1595篇 |
2007年 | 1388篇 |
2006年 | 1308篇 |
2005年 | 1088篇 |
2004年 | 910篇 |
2003年 | 698篇 |
2002年 | 704篇 |
2001年 | 603篇 |
2000年 | 471篇 |
1999年 | 426篇 |
1998年 | 333篇 |
1997年 | 336篇 |
1996年 | 293篇 |
1995年 | 244篇 |
1994年 | 226篇 |
1993年 | 165篇 |
1992年 | 115篇 |
1991年 | 136篇 |
1990年 | 112篇 |
1989年 | 78篇 |
1988年 | 79篇 |
1987年 | 68篇 |
1986年 | 53篇 |
1985年 | 36篇 |
1984年 | 30篇 |
1983年 | 29篇 |
1982年 | 27篇 |
1981年 | 18篇 |
1980年 | 16篇 |
1979年 | 6篇 |
1976年 | 6篇 |
1975年 | 8篇 |
1959年 | 5篇 |
1957年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Exact closed-form solutions are derived that completely characterize the effective behavior of a composite material made of elastic-perfectly plastic parallel plane layers perfectly bonded together. The derivation is framed within a rigorous theory of homogenization for elastoplastic composites, and based on the fundamental fact that the in-plane part of the strain tensor and the out-of-plane part of the stress tensor are uniform throughout the composite provided no free-edge effects occur. The obtained expressions are coordinate-free and valid in the general anisotropic case. As an example, a layered composite material with isotropic constituents is examined in detail. 相似文献
92.
Yue Shao Hong-Ping Zhao Xi-Qiao Feng Huajian Gao 《Journal of the mechanics and physics of solids》2012,60(8):1400-1419
Studying the structure–property relation of biological materials can not only provide insight into the physical mechanisms underlying their superior properties and functions but also benefit the design and fabrication of advanced biomimetic materials. In this paper, we present a microstructure-based fracture mechanics model to investigate the toughening effect due to the crack-bridging mechanism of platelets. Our theoretical analysis demonstrates the crucial contribution of this mechanism to the high toughness of nacre. It is found that the fracture toughness of nacre exhibits distinct dependence on the sizes of platelets, and the optimized ranges for the thickness and length of platelets required to achieve higher fracture toughness are given. In addition, the effects of such factors as the mechanical properties of the organic phase (or interfaces), the effective elastic modulus of nacre, and the stacking pattern of platelets are also examined. Finally, some guidelines for the biomimetic design of novel materials are proposed based on our theoretical analysis. 相似文献
93.
94.
95.
96.
97.
98.
Lipid profiling of human plasma from peritoneal dialysis patients using an improved 2D (NP/RP) LC-QToF MS method 总被引:1,自引:0,他引:1
Min Li Baosheng Feng Yuan Liang Wei Zhang Yu Bai Wen Tang Tao Wang Huwei Liu 《Analytical and bioanalytical chemistry》2013,405(21):6629-6638
An improved online two-dimensional liquid chromatography-quadrupole time-of-flight mass spectrometry (2D LC-QToF MS) system was developed for the lipid profiling of human plasma, in which different lipid classes were separated by the first dimensional normal-phase (NP) LC and different lipid molecular species were separated by the second dimensional reversed-phase (RP) LC. This 2D LC-QToF MS system was built based on a ten-port, two-position valve as the interface, the conditions of which had been optimized and discussed in detail. As two loops were used to trap and transfer the first dimensional elute to the second dimension separately, this new interface suppressed the sample band broadening in the first dimensional column, increased the recovery and repeatability of 2D LC interface, and offered the possibility for the realization of not-stop-flow NP/RP 2D LC system. Finally, 190 endogenous lipid species out of 10 lipid classes were determined within a single run from the plasma of peritoneal patients. This method was also applied to identify the difference in lipid profile between plasma from peritoneal dialysis patients with bad volume status and peritoneal dialysis patients with good volume status. The discovery of 30 potential biomarkers would be helpful to the malnutrition, inflammation, and atherosclerosis syndrome investigation. 相似文献
99.
100.
Feng Yu 《International journal of quantum chemistry》2013,113(21):2355-2360
The intermolecular interactions of formic acid (HCOOH) with benzene (C6H6) have been investigated using localized molecular orbital energy decomposition analyses (LMO‐EDA) with ab initio MP2 and several double‐hybrid density functionals. The molecular geometries of five HCOOH…C6H6 complexes and corresponding benchmark total interaction energies at the CCSD(T)/CBS level are taken from literature (Zhao et al., J. Chem. Theory Comput. 2009, 5, 2726). According to the results of LMO‐EDA with the MP2 method, the dispersion energies are found to be as important as the electrostatic energies for the total interaction energies of the five HCOOH…C6H6 complexes. Based on LMO‐EDA with the double‐hybrid density functionals of B2PLYP, B2K‐PLYP, B2T‐PLYP, and B2GP‐PLYP computations, two new parameters for the framework of B2PLYP are extrapolated. These two new parameters are tested with other 10 complexes involving C6H6 (Crittenden, J. Phys. Chem. A 2009, 113, 1663), and they perform well on predicting the corresponding total interaction energies. Interestingly, these two new parameters for the framework of B2PLYP also perform well on the noncovalent complexation energies database (NCCE31/05) developed by Truhlar's group (Zhao and Truhlar, J. Phys. Chem. A 2005, 109, 5656). Therefore, these two new parameters appear to be suitable for investigating the noncovalent interactions, and they are denoted as B2N‐PLYP, where N stands for the noncovalent interaction. This study is expected to provide new insight into the derivation of double‐hybrid density functionals for studying the noncovalent interactions. © 2013 Wiley Periodicals, Inc. 相似文献