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   307743篇
  免费   4298篇
  国内免费   1080篇
化学   166003篇
晶体学   3496篇
力学   12890篇
综合类   7篇
数学   36059篇
物理学   94666篇
  2020年   1986篇
  2019年   1954篇
  2018年   1967篇
  2017年   1875篇
  2016年   3859篇
  2015年   3236篇
  2014年   4424篇
  2013年   13982篇
  2012年   10741篇
  2011年   13369篇
  2010年   8282篇
  2009年   8256篇
  2008年   12340篇
  2007年   12577篇
  2006年   12225篇
  2005年   11161篇
  2004年   10039篇
  2003年   8852篇
  2002年   8163篇
  2001年   9668篇
  2000年   7126篇
  1999年   5527篇
  1998年   4295篇
  1997年   4303篇
  1996年   4290篇
  1995年   4235篇
  1994年   3999篇
  1993年   3833篇
  1992年   4307篇
  1991年   4188篇
  1990年   3893篇
  1989年   3729篇
  1988年   4029篇
  1987年   3684篇
  1986年   3595篇
  1985年   5258篇
  1984年   5343篇
  1983年   4306篇
  1982年   4688篇
  1981年   4732篇
  1980年   4470篇
  1979年   4622篇
  1978年   4626篇
  1977年   4597篇
  1976年   4569篇
  1975年   4459篇
  1974年   4323篇
  1973年   4495篇
  1972年   2537篇
  1971年   1841篇
排序方式: 共有10000条查询结果,搜索用时 18 毫秒
81.
Non-equilibrium self-assembly is ubiquitous in physico-chemical and biological systems, and manifests itself at different scales, ranging from the molecular to the cosmological. The formation of microtubules, gels, cells and living beings among many others takes place through self-assembly under nonequilibrium conditions. We propose a general thermodynamic non-equilibrium model to understand the formation of assembled structures such as gels and Liesegang patterns and at the same time able to describe the kinetics and the energetics of the structure formation process. The model is supported for a global mechanism to obtain self-assembled structures from building blocks via activation, deactivation, assembly, and disassembly processes. It is proposed that the resulting structures can be characterised by a structural parameter. Our model may contribute to a better understanding of non-equilibrium self-assembly processes and give deeper insight as to how to obtain a specific structural architecture to materials, such as hydrogels which are of great importance in the design of advanced devices and novel materials.  相似文献   
82.
X-ray astronomy and ground-based atomic physics have a long history of fruitful collaboration: Sound understanding of the underlying atomic physics is the key to reliable interpretation of the spectra from celestial sources; conversely, astronomical spectra have been used to benchmark and advance atomic physics. This interplay is about to become even more important as we enter a new era of high-resolution X-ray astrophysics with large effective collection area. Although high-resolution observations with the gratings on the Chandra and XMM-Newton observatories continue to drive new science, upcoming planned and proposed missions will open up new discovery space in the near future that is currently challenging to access: high-resolution spectroscopy on extended sources, in the Fe K band, and on short time scales. This review summarizes open questions in these areas and the design parameters for the Hitomi, XRISM, Athena, and Arcus observatories. The expected high quality of spectra taken with these observatories puts new constraints on the accuracy of atomic reference data required to take full advantage of the diagnostic potential of these spectra.  相似文献   
83.
Mechanics of Composite Materials - Commercial γ ? Al2O3 particles, Al2O3 n, and synthesized Al2O3 doped with iron oxide (Al2O3 Fe) were used as reinforcements to enhance the toughness of...  相似文献   
84.
ABSTRACT

To understand the practical effects of pressure-transmitting media (PTM) on neutron diffraction using Paris–Edinburgh presses, diffraction patterns of MgO were collected to approximately 20?GPa using PTMs of Pb, AgCl, 4:1 methanol–ethanol (ME) mixture with and without heating, N2, and Ar. Hydrostaticity in the sample chamber estimated from the MgO 220 peak width improves in the order of Pb, AgCl, Ar, ME mixture, N2, and the heated ME mixture. Unlike previous results using diamond anvil cells, the unheated ME mixture is superior to Ar even after freezing, probably due to the cup on the anvil face. Considering these results and the sizable coherent scattering of Ne, which would show good hydrostaticity, we conclude that the ME mixture (preferably the heated one) is the best PTM in neutron experiments up to 20?GPa, while Ar can be substituted when a sample is reactive to alcohols.  相似文献   
85.
Guerrero  J. E.  Sanguineti  M.  Wittkowski  K. 《Meccanica》2020,55(10):1917-1947
Meccanica - Traditional winglets are designed as fixed devices attached at the tips of the wings. The primary purpose of the winglets is to reduce the lift-induced drag, therefore improving...  相似文献   
86.
The European Physical Journal A - A deterministic treatment of sequential neutron emission, based on recursive equations of the residual temperatures, was applied to numerous fission cases (i.e. 49...  相似文献   
87.
Journal of Thermal Analysis and Calorimetry - The steady flow of a nanofluid (mixture of titanium dioxide and water) in a rectangular channel under the influence of an inclined magnetic field is...  相似文献   
88.
Li  Qiang  Schultz  Paul  Lin  Wei  Kurths  Jürgen  Ji  Peng 《Nonlinear dynamics》2020,102(2):653-665
Nonlinear Dynamics - A complex system’s structural–dynamical interplay plays a profound role in determining its collective behavior. Irregular behavior in the form of macroscopic chaos,...  相似文献   
89.
To assess the bioequivalence of two zolpidem hemitartrate formulations in 30 healthy volunteers. Plasma samples were obtained over a 24 h period. Plasma concentrations of zolpidem were analyzed by liquid chromatography coupled to tandem mass spectrometry with positive ion electrospray ionization using multiple reaction monitoring. Values of peak concentration (Cmax), area under curve (AUC), half-life, elimination constant, volume of distribution and clearance showed statistically significant differences when comparing women (604.34 ng h/ml, 127.36 ng/ml, 4.4 h, 0.18 1/h, 50.56 L and 8.55 L/h, respectively) and men (276.1 ng h/ml, 70.9 ng/ml, 3.3 h, 0.26 1/h, 91.42 L and 24.34 L/h, respectively), receiving the same dose (5 mg), respectively. The geometric means with corresponding 90% confidence interval for Test/Reference percentage ratios were 99.73% (CI 93.69–106.16) for Cmax, 97.44% (90% CI = 91.85–103.37%) for area under curve of plasma concentration until the last concentration observed (AUClast) and 98.30% (90% CI = 92.48–104.49) for the area under curve between the first sample (pre-dosage) and infinity (AUC0–inf). Since the 90% CI for AUClast, AUC0–inf and Cmax ratios were within the 80–125% interval proposed by the US Food and Drug Administration, it was concluded that zolpidem hemitartrate formulation (5 mg orodispersible tablet) is bioequivalent to the zolpidem hemitartrate formulation (Patz SL 5 mg sublingual tablet) with regard to both the rate and the extent of absorption. A new formulation of zolpidem 2.5 mg may be useful in women for the same clinical benefits as the 5 mg formulation in men.  相似文献   
90.
A rapid, selective, and sensitive liquid chromatography coupled with tandem mass spectrometry (MS/MS) method was developed and validated for the quantitation of the novel CDK5 inhibitor ‘20–223' in mouse plasma. Separation of analytes was achieved by a reverse-phase ACE Excel C18 column (1.7 μm, 100 × 2.1 mm) with gradient elution using 0.1% formic acid (FA) in methanol and 0.1% FA as the mobile phase. Analytes were monitored by MS/MS with an electrospray ionization source in the positive multiple reaction monitoring mode. The MS/MS response was linear over the concentration range 0.2–500 ng/mL for 20–223. The within- and between-batch precision were within the acceptable limits as per Food and Drug Administration guidelines. The validated method was successfully applied to plasma protein binding and in vitro metabolism studies. Compound 20–223 was highly bound to mouse plasma proteins (>98% bound). Utilizing mouse S9 fractions, in vitro intrinsic clearance (CLint) was 24.68 ± 0.99 μL/min/mg protein. A total of 12 phase I and II metabolites were identified with hydroxylation found to be the major metabolic pathway. The validate method required a low sample volume, was linear from 0.2 to 500 ng/mL, and had acceptable accuracy and precision.  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