全文获取类型
收费全文 | 31566篇 |
免费 | 171篇 |
国内免费 | 292篇 |
专业分类
化学 | 12150篇 |
晶体学 | 270篇 |
力学 | 1510篇 |
综合类 | 12篇 |
数学 | 9394篇 |
物理学 | 8693篇 |
出版年
2023年 | 36篇 |
2022年 | 65篇 |
2021年 | 131篇 |
2020年 | 117篇 |
2019年 | 89篇 |
2018年 | 1238篇 |
2017年 | 1485篇 |
2016年 | 829篇 |
2015年 | 630篇 |
2014年 | 581篇 |
2013年 | 786篇 |
2012年 | 3306篇 |
2011年 | 2512篇 |
2010年 | 1914篇 |
2009年 | 1636篇 |
2008年 | 718篇 |
2007年 | 766篇 |
2006年 | 776篇 |
2005年 | 4587篇 |
2004年 | 4022篇 |
2003年 | 2401篇 |
2002年 | 590篇 |
2001年 | 327篇 |
2000年 | 108篇 |
1999年 | 196篇 |
1998年 | 138篇 |
1997年 | 103篇 |
1996年 | 78篇 |
1995年 | 61篇 |
1994年 | 63篇 |
1993年 | 37篇 |
1992年 | 175篇 |
1991年 | 167篇 |
1990年 | 143篇 |
1989年 | 115篇 |
1988年 | 110篇 |
1987年 | 65篇 |
1986年 | 52篇 |
1985年 | 45篇 |
1984年 | 38篇 |
1983年 | 35篇 |
1979年 | 39篇 |
1976年 | 81篇 |
1975年 | 46篇 |
1974年 | 41篇 |
1973年 | 49篇 |
1972年 | 39篇 |
1969年 | 37篇 |
1968年 | 35篇 |
1966年 | 37篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
1.
Mohammad A. Khalilzadeh Soo Young Kim Ho Won Jang Rafael Luque Rajender S. Varma Richard A. Venditti Mohammadreza Shokouhimehr 《Materials Today Chemistry》2022
The requirement of green and sustainable materials to prepare heterogeneous catalysts has intensified for practical reasons over the past few decades. Carbohydrates are possibly the most plentiful and renewable organic materials in nature with inimitable physiochemical properties, plausible low-cost and large-scale production, and sustainability features could be exploited in the generation of nanostructured heterogeneous catalysts. This review article outlines the organic transformations catalyzed by diverse carbohydrate-based nanostructured catalysts in greener and environmentally friendly processes. Selected examples are highlighted for a variety of organic reactions exploiting the proposed catalysts’ reactivity and reusability, and interactions with the intrinsic nature of the applied carbohydrate supports; advantages and speculated challenges of the introduced catalysts are deliberated as well. 相似文献
2.
Matt Visser Carlos Barceló Stefano Liberati 《General Relativity and Gravitation》2002,34(10):1719-1734
Condensed matter systems, such as acoustics in flowing fluids, light in moving dielectrics, or quasiparticles in a moving superfluid, can be used to mimic aspects of general relativity. More precisely these systems (and others) provide experimentally accessible models of curved-space quantum field theory. As such they mimic kinematic aspects of general relativity, though typically they do not mimic the dynamics. Although these analogue models are thereby limited in their ability to duplicate all the effects of Einstein gravity they nevertheless are extremely important—they provide black hole analogues (some of which have already been seen experimentally) and lead to tests of basic principles of curved-space quantum field theory. Currently these tests are still in the realm of gedanken-experiments, but there are plausible candidate models that should lead to laboratory experiments in the not too distant future. 相似文献
3.
Julia K Pruns Jens-Peter Vietzke Manfred Strassner Claudius Rapp Ulrich Hintze Wilfried A K?nig 《Rapid communications in mass spectrometry : RCM》2002,16(3):208-211
A new solvent-free sample preparation method using silver trifluoroacetate (AgTFA) was developed for the analysis of low molecular weight paraffins and microcrystalline waxes by laser desorption/ionization time-of-flight mass spectrometry (LDI-TOFMS). Experiments show that spectral quality can be enhanced by dispersing AgTFA directly in liquid paraffins without the use of additional solvents. This preparation mixture is applied directly to the MALDI probe. Solid waxes could be examined by melting prior to analysis. The method also provides sufficiently reproducible spectra that peak area ratios between mono- and bicyclic alkane peaks indicated variations in the cycloalkane content of paraffin samples. Dehydrogenation of hydrocarbons observed during the desorption/ionization process was studied by analysis of alkane standards. 相似文献
4.
Pierluigi Contucci Sandro Graffi Stefano Isola 《Journal of statistical physics》2002,106(5-6):895-914
For the long-range deterministic spin models with glassy behaviour of Marinari, Parisi and Ritort we prove weighted factorization properties of the correlation functions which represent the natural generalization of the factorization rules valid for the Curie–Weiss case. 相似文献
5.
The versatile behavior of a trihydrazidophosphoradamantane allowing the synthesis of a variety of neutral, mono- or di-cationic water-soluble molecules of potential interest for biphasic catalysis is reported. 相似文献
6.
In this paper we construct an example of a word metric on an infinite cyclic subgroup. This example shows that subexponential
distortion does not obstruct non-trivial growth of connected radii. This answers a question of Gromov [6]. The constructed
metric has other pathological properies. Specifically, its asymptotic cone depends on the choice of ultrafilter and scaling
sequence.
The work has been partially supported by the Swiss National Science Foundation. 相似文献
7.
We build a metric space which is homeomorphic to a Cantor set but cannot be realized as the attractor of an iterated function system. We give also an example of a Cantor set K in R3 such that every homeomorphism f of R3 which preserves K coincides with the identity on K. 相似文献
8.
Stefano Vannucci 《Annals of Operations Research》2002,109(1-4):99-127
Stability properties of several governance structures are studied by means of their effectivity functions. It is shown that (strong) stability of a governance structure is mainly determined by the collegial nature of the underlying assembly's decision rule. 相似文献
9.
Milan Medved? 《Journal of Mathematical Analysis and Applications》2002,267(2):643-650
A criterion for the nonexplosion of solutions to semilinear evolution equations on Banach spaces is proved. The result is obtained by applying a modification of the Bihari type inequality to the case of a weakly singular nonlinear integral inequality. 相似文献
10.
We consider the one-dimensional steady-state semiconductor deviceequations modelling a pnpn device. There are two relevant scalingsof the equations corresponding to small and large applied voltages.In both scalings, the semiconductor equations can be consideredas singularly perturbed. It turns out that the small-voltagescaling breaks down for current values between two saturationcurrents. In that interval, the large-voltage scaling has tobe employed. For both scalings, we derive the first-order termsof an asymptotic expansion and show that the reduced problemhas a solution. An example verifies that the current-voltagecurves obtained have the expected qualitative structure. 相似文献