全文获取类型
收费全文 | 94153篇 |
免费 | 9375篇 |
国内免费 | 12956篇 |
专业分类
化学 | 78812篇 |
晶体学 | 2178篇 |
力学 | 3048篇 |
综合类 | 1043篇 |
数学 | 8854篇 |
物理学 | 22549篇 |
出版年
2024年 | 225篇 |
2023年 | 1039篇 |
2022年 | 3380篇 |
2021年 | 3178篇 |
2020年 | 2953篇 |
2019年 | 2709篇 |
2018年 | 2180篇 |
2017年 | 2434篇 |
2016年 | 3252篇 |
2015年 | 3270篇 |
2014年 | 3949篇 |
2013年 | 6708篇 |
2012年 | 5947篇 |
2011年 | 4977篇 |
2010年 | 4393篇 |
2009年 | 5334篇 |
2008年 | 5714篇 |
2007年 | 5997篇 |
2006年 | 5179篇 |
2005年 | 4318篇 |
2004年 | 4211篇 |
2003年 | 3856篇 |
2002年 | 5857篇 |
2001年 | 3007篇 |
2000年 | 2636篇 |
1999年 | 2164篇 |
1998年 | 1955篇 |
1997年 | 1534篇 |
1996年 | 1547篇 |
1995年 | 1360篇 |
1994年 | 1267篇 |
1993年 | 1075篇 |
1992年 | 1097篇 |
1991年 | 716篇 |
1990年 | 606篇 |
1989年 | 493篇 |
1988年 | 483篇 |
1987年 | 362篇 |
1986年 | 359篇 |
1985年 | 492篇 |
1984年 | 364篇 |
1983年 | 235篇 |
1982年 | 382篇 |
1981年 | 562篇 |
1980年 | 517篇 |
1979年 | 541篇 |
1978年 | 432篇 |
1977年 | 336篇 |
1976年 | 284篇 |
1973年 | 216篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
221.
We investigate the effects of adding uniformity requirements to concepts in computable structure theory such as computable categoricity (of a structure) and intrinsic computability (of a relation on a computable structure). We consider and compare two different notions of uniformity, previously studied by Kudinov and by Ventsov. We discuss some of their results and establish new ones, while also exploring the connections with the relative computable structure theory of Ash, Knight, Manasse, and Slaman and Chisholm and with previous work of Ash, Knight, and Slaman on uniformity in a general computable structure-theoretical setting. 相似文献
222.
In this paper, we study the stability conditions of the MMAP[K]/G[K]/1/LCFS preemptive repeat queue. We introduce an embedded Markov chain of matrix M/G/1 type with a tree structure and identify conditions for the Markov chain to be ergodic. First, we present three conventional methods for the stability problem of the queueing system of interest. These methods are either computationally demanding or do not provide accurate information for system stability. Then we introduce a novel approach that develops two linear programs whose solutions provide sufficient conditions for stability or instability of the queueing system. The new approach is numerically efficient. The advantages and disadvantages of the methods introduced in this paper are analyzed both theoretically and numerically. 相似文献
223.
两相同部件温贮备可修的人机系统解的性质分析 总被引:5,自引:1,他引:4
郭卫华 《数学的实践与认识》2003,33(7):88-95
本文首先用强连续算子半群理论证明了两相同部件温贮备可修的人机系统动态非负解的存在唯一性 ,然后证明了 0是系统主算子的本征值 ,并得到 0本征值对应的本征向量是正的 ,从而系统存在稳态正解 . 相似文献
224.
Determination of electronic structure of ozone related geometry is the main subject in this research. The proposed electronic structure must satisfy the experimental geometry, explain the excellent oxidizing properties of ozone, and can also explain the capability of additional reaction with unsaturated hydrocarbons. The potential energy surface of singlet and triplet state of ozone has been studied in order to check the correctness of the proposed structure. The proposed electronic structure of ozone is capable of explaining the oxidizing behavior of ozone in visible wavelength (daylight) 430–700 nm. For comparison, the other proposed structure of ozone in literature such as Pauling, Linnett and Weinhold has also been discussed. The main method used in this research is well-known density functional procedure, B3LYP, which takes the electron correlation aspect into consideration. The polarization and diffused functions are included in the basis set, 6-311++G**. The obtained geometry is a bent and cumulated double bond with inter-bond angle 118.42° (1.39%), and bond length 1.256 Å (1.72%). The obtained results revealed that frontier orbital theory is a proper tool for explaining the addition reaction. 相似文献
225.
J. T. Hoeft M. Polcik D. I. Sayago M. Kittel R. Terborg R. L. Toomes J. Robinson D. P. Woodruff M. Pascal G. Nisbet C. L. A. Lamont 《Surface science》2003,540(2-3):441-456
The local adsorption geometry of CO adsorbed in different states on Ni(1 0 0) and on Ni(1 0 0) precovered with atomic hydrogen has been determined by C 1s (and O 1s) scanned-energy mode photoelectron diffraction, using the photoelectron binding energy changes to characterise the different states. The results confirm previous spectroscopic assignments of local atop and bridge sites both with and without coadsorbed hydrogen. The measured Ni–C bondlengths for the Ni(1 0 0)/CO states show an increase of 0.16 ± 0.04 Å in going from atop to bridge sites, while comparison with similar results for Ni(1 1 1)/CO for threefold coordinated adsorption sites show a further lengthening of the bond by 0.05 ± 0.04 Å. These changes in the Ni–CO chemisorption bondlength with bond order (for approximately constant adsorption energy) are consistent with the standard Pauling rules. However, comparison of CO adsorbed in the atop geometry with and without coadsorbed hydrogen shows that the coadsorption increases the Ni–C bondlength by only 0.06 ± 0.04 Å, despite the decrease in adsorption energy of a factor of 2 or more. This result is also reproduced by density functional theory slab calculations. The results of both the experiments and the density functional theory calculations show that CO adsorption onto the Ni(1 0 0)/H surface is accompanied by significant structural modification; the low desorption energy may then be attributed to the energy cost of this restructuring rather than weak local bonding. 相似文献
226.
François Ledrappier Mark Pollicott 《Bulletin of the Brazilian Mathematical Society》2005,36(2):143-176
In this paper we study the ergodic properties of the linear action of lattices Γ of SL(2,ℚp) on ℚp × ℚp and distribution results for orbits of Γ. Following Serre, one can define a “geodesic flow” for an associated tree (actually
associated to GL(2,ℚp)). The approach we use is based on an extension of this approach to “frame flows” which are a natural compact group extension
of the geodesic flow. 相似文献
227.
The content of residual monomers is one of the most important characteristics of polymer dispersions. As a result of the similar physicochemical parameters of ethyl acrylate and methyl methacrylate, it is very difficult to determine the residual monomers in acrylate dispersions obtained by emulsion polymerization of both monomers. Gas chromatography with capillary columns, however, permits separation of these monomers and their quantitative determination in acrylate dispersions. 相似文献
228.
229.
Some nickel, copper, and silver salts or complexes are efficient catalysts for the oxidation of benzylic ethers with oxygen in 1,2-dimethoxyethane. Salts of the weakly coordinating anion trifluoroacetate are particularly efficient, approaching (and, in some cases, improving) the yields obtained with cobalt(II) chloride, the best catalyst so far reported. 相似文献
230.
Biswarup Mukhopadhyaya 《Pramana》1998,51(1-2):181-190
The observable consequences of gauge-mediated supersymmetry breaking (GMSB) are reviewed here. Implications of scenarios both
with a neutralino and a slepton as the next lightest supersymmetric particle (NLSP) are surveyed in relation to hadronic ande
+
e
- colliders. We also discuss the phenomenological consequences of the NLSP decaying slowly, giving rise to delayed events in
the detectors.The importance of distinguishing signals of GMSB models from those of the commonly discussed supergravity-type
theories is emphasized. 相似文献