全文获取类型
收费全文 | 15076篇 |
免费 | 413篇 |
国内免费 | 114篇 |
专业分类
化学 | 10702篇 |
晶体学 | 234篇 |
力学 | 311篇 |
综合类 | 1篇 |
数学 | 2532篇 |
物理学 | 1823篇 |
出版年
2021年 | 140篇 |
2020年 | 162篇 |
2019年 | 168篇 |
2018年 | 123篇 |
2017年 | 115篇 |
2016年 | 305篇 |
2015年 | 291篇 |
2014年 | 276篇 |
2013年 | 695篇 |
2012年 | 711篇 |
2011年 | 827篇 |
2010年 | 471篇 |
2009年 | 384篇 |
2008年 | 793篇 |
2007年 | 806篇 |
2006年 | 779篇 |
2005年 | 744篇 |
2004年 | 617篇 |
2003年 | 495篇 |
2002年 | 570篇 |
2001年 | 181篇 |
2000年 | 198篇 |
1999年 | 186篇 |
1998年 | 178篇 |
1997年 | 219篇 |
1996年 | 252篇 |
1995年 | 178篇 |
1994年 | 166篇 |
1993年 | 189篇 |
1992年 | 182篇 |
1991年 | 132篇 |
1990年 | 160篇 |
1989年 | 137篇 |
1988年 | 143篇 |
1987年 | 128篇 |
1986年 | 133篇 |
1985年 | 235篇 |
1984年 | 215篇 |
1983年 | 168篇 |
1982年 | 265篇 |
1981年 | 203篇 |
1980年 | 204篇 |
1979年 | 168篇 |
1978年 | 175篇 |
1977年 | 171篇 |
1976年 | 160篇 |
1975年 | 139篇 |
1974年 | 164篇 |
1973年 | 146篇 |
1972年 | 98篇 |
排序方式: 共有10000条查询结果,搜索用时 250 毫秒
31.
Summary We prove convergence and error estimates in Sobolev spaces for the collocation method with tensor product splines for strongly elliptic pseudodifferential equations on the torus. Examples of applications include elliptic partial differential equations with periodic boundary conditions but also the classical boundary integral operators of potential theory on torus-shaped domains in three or more dimensions. For odd-degree splines, we prove convergence of nodal collocation for any strongly elliptic operator. For even-degree splines and midpoint collocation, we find an additional condition for the convergence which is satisfied for the classical boundary integral operators. Our analysis is a generalization to higher dimensions of the corresponding analysis of Arnold and Wendland [4]. 相似文献
32.
Gordon W. Rewcastle Hamish S. Sutherland Claudette A. Weir Adrian G. Blackburn William A. Denny 《Tetrahedron letters》2005,46(50):8719-8721
A novel two-step synthesis of isonitrosoacetanilides [2-(hydroxyimino)-N-phenylacetamides] has been developed, involving the initial acylation of aniline derivatives with 2,2-diacetoxyacetyl chloride, followed by reaction with hydroxylamine hydrochloride. The method works equally well with a variety of different aniline derivatives, including those with poor aqueous solubility and those containing electron rich ortho-substituents, neither of which react well under traditional conditions. 相似文献
33.
Gary S. Nichol William Clegg 《Acta Crystallographica. Section C, Structural Chemistry》2007,63(10):o609-o612
The title compound [systematic name: ammonium pyrimidine‐2,4‐5,6(1H,3H)‐tetrone 5‐oximate], NH4+·C4H2N3O4−, crystallizes from water in the triclinic space group P and is ismorphous with a known rubidium complex [Gillier (1965). Bull. Soc. Chim. Fr. pp. 2373–2384]. The principal feature of the structure is hydrogen bonding; each ammonium H atom acts as a bifurcated donor and three of the four violurate O atoms are bifurcated acceptors, with the fourth acting as a trifurcated acceptor. The pattern of hydrogen bonding around the cation is very similar to the rubidium coordination environment in the related structure. The violurate anions pack as hydrogen‐bonded crinkled tapes, which are linked and separated by the ammonium cations to give a compact three‐dimensional structure. 相似文献
34.
T. Bernhard 《Surface science》2006,600(9):1877-1883
The structure and magnetism of thin epitaxial Fe layers grown on Cu(0 0 1) is investigated by grazing scattering of fast H and He atoms. Information on the atomic structure of the film and substrate surfaces is obtained by making use of ion beam triangulation with protons. The magnetic behavior is studied via the polarization of light emitted after capture of spin-polarized electrons into excited atomic terms during scattering of He atoms. For the formation of bcc(1 1 0)-like Fe films at higher coverages, we detect differences in structural and magnetic properties for room and low temperature growth. We suggest that the crystalline structure depends on the film morphology and that Cu impurities affect the magnetic properties. 相似文献
35.
This report focuses on a theoretical study of the cobalt-cabon bond activation mechanism in Vitamin B12, its co enzyme complexes, and model compounds such as cobalamins (Cbl), cobaloximes and cobalt porphyrins. In particular, emphasis is placed on the nucleotide loop and its role in the base on and base off mechanism. 相似文献
36.
We provide an approximate analysis of the transient sojourn time for a processor sharing queue with time varying arrival and
service rates, where the load can vary over time, including periods of overload. Using the same asymptotic technique as uniform
acceleration as demonstrated in [12] and [13], we obtain fluid and diffusion limits for the sojourn time of the Mt/Mt/1 processor-sharing queue. Our analysis is enabled by the introduction of a “virtual customer” which differs from the notion
of a “tagged customer” in that the former has no effect on the processing time of the other customers in the system. Our analysis
generalizes to non-exponential service and interarrival times, when the fluid and diffusion limits for the queueing process
are known. 相似文献
37.
We show that the tenure lengths for managers of sport teams follow a power law distribution with an exponent between 2 and 3. We develop a simple theoretical model which replicates this result. The model demonstrates that the empirical phenomenon can be understood as the macroscopic outcome of pairwise interactions among managers in a league, threshold effects in managerial performance evaluation, competitive market forces, and luck at the microscopic level. 相似文献
38.
Ohne Zusammenfassung 相似文献
39.
Zhijian Zhao William H. LeisterKimberly A. Strauss David D. WisnoskiCraig W. Lindsley 《Tetrahedron letters》2003,44(6):1123-1127
By the application of microwave technology, a general protocol has been developed for the rapid synthesis of diverse 3,5,6-trisubstituted 1,2,4-triazines in excellent yield and purity, including many previously unknown 3-heterocyclic-1,2,4-triazines. 相似文献
40.
Wenbing Hu Alexander Buzin Jar‐Shyong Lin Bernhard Wunderlich 《Journal of Polymer Science.Polymer Physics》2003,41(4):403-417
The annealing at 373 K of ultrastrong, gel‐spun polyethylene (PE) has been studied. At this temperature, the fibers show no significant shrinkage. Still, a significant decrease in the mechanical properties is observed. The fibers have been analyzed with differential scanning calorimetry (DSC), temperature‐modulated differential scanning calorimetry (TMDSC), atomic force microscopy (AFM), and small‐angle X‐ray scattering (SAXS). During the annealing, the glass transition of the intermediate phase is exceeded, as shown by DSC. When split for structure analysis by AFM, the annealed fibers undergo plastic deformation around the base fibrils instead of brittle fracture. The quasi‐isothermal TMDSC experiments are compared to the minor structural changes seen with SAXS and AFM. The loss of performance of the PE fibers at 373 K is suggested to be caused by the oriented intermediate phase, and not by major changes in the structure or morphology. The overall metastable, semicrystalline structure is shown by TMDSC to posses local regions that can melt reversibly. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 403–417, 2003 相似文献