全文获取类型
收费全文 | 11265篇 |
免费 | 929篇 |
国内免费 | 1291篇 |
专业分类
化学 | 9175篇 |
晶体学 | 160篇 |
力学 | 67篇 |
综合类 | 38篇 |
数学 | 2958篇 |
物理学 | 1087篇 |
出版年
2024年 | 23篇 |
2023年 | 120篇 |
2022年 | 139篇 |
2021年 | 167篇 |
2020年 | 278篇 |
2019年 | 322篇 |
2018年 | 232篇 |
2017年 | 267篇 |
2016年 | 292篇 |
2015年 | 417篇 |
2014年 | 520篇 |
2013年 | 992篇 |
2012年 | 683篇 |
2011年 | 648篇 |
2010年 | 585篇 |
2009年 | 651篇 |
2008年 | 753篇 |
2007年 | 677篇 |
2006年 | 576篇 |
2005年 | 547篇 |
2004年 | 519篇 |
2003年 | 473篇 |
2002年 | 643篇 |
2001年 | 342篇 |
2000年 | 345篇 |
1999年 | 278篇 |
1998年 | 264篇 |
1997年 | 214篇 |
1996年 | 178篇 |
1995年 | 145篇 |
1994年 | 148篇 |
1993年 | 120篇 |
1992年 | 105篇 |
1991年 | 84篇 |
1990年 | 87篇 |
1989年 | 95篇 |
1988年 | 73篇 |
1987年 | 53篇 |
1986年 | 48篇 |
1985年 | 52篇 |
1984年 | 47篇 |
1983年 | 33篇 |
1982年 | 36篇 |
1981年 | 34篇 |
1980年 | 35篇 |
1979年 | 31篇 |
1978年 | 21篇 |
1974年 | 14篇 |
1973年 | 15篇 |
1971年 | 16篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
101.
The proportional hazards regression model, when subjects enter the study in a staggered fashion, is studied. A strong martingale approach is used to model the two-time parameter counting processes. It is shown that well-known univariate results such as weak convergence and martingale inequalities can be extended to this two-dimensional model. Strong martingale theory is also used to prove weight convergence of a general weighted goodness-of-fit process and its weighted bootstrap counterpart. 相似文献
102.
LIKAITAI HEYINNIAN XIANGYIMIN 《高校应用数学学报(英文版)》1994,9(1):11-30
This paper deals with the inertial manifold and the approximate inertial manifold concepts of the Navier-Stokes equations with nonhomogeneous boundary conditions and inertial algorithm. Furtheremore, we provide the error estimates of the approximate solutions of the Navier-Stokes Equations. 相似文献
103.
第Ⅰ种强度不对称三态叠加多模叠加态光场N次方Y压缩—第一正交相位分量的压缩情况 总被引:2,自引:0,他引:2
根据量子力学中的线性叠加原理,构造了由三个强度不等的多模相干态光场|{Zj(A)}>q、|{Zj(B)}>q和|{Zj(C)}>q的线性叠加所组成的第Ⅰ种强度不对称三态叠加多模叠加态光场|ψl(ABC)>q.利用多模压缩态理论,研究了态|ψl(ABC)>q的第一正交方分量(即磁场分量)的广义非线性等幂次N次方Y压缩特性.结果发现:①在上述各多模相干态光场中各模的强度和各模的初始相位各不相等的情况下,态|ψl(ABC)>q的第一正交分量-磁场分量在一定的条件下,总可呈现出周期性变化的、任意等幂次的N次方Y压缩效应;②当上述各多模相干态光场的强度和各模的初始相位相等时,态|ψl(ABC)>q的磁场分量的N次方Y压缩现象消失,态|ψl(ABC)>q可恒处于等幂次N-Y最小测不准态. 相似文献
104.
Sander C. Hille 《Integral Equations and Operator Theory》2005,53(4):597-601
A linear semigroup in a Banach space induces a linear semigroup on a Banach space that can be continuously embedded in the
former such that its image is invariant. This restriction need not be strongly continuous, although the original semigroup
is strongly continuous. We show that norm or weak compactness of partial orbits is a necessary and sufficient condition for
strong continuity of the restriction of a C0-semigroup. We then show that if the embedded Banach space is reflexive and the norms of the restricted semigroup operators
are bounded near the initial time, then the restricted semigroup is strongly continuous. 相似文献
105.
Zhigang Zhang Jianping Deng Weiguo Zhao Jianmin Wang Wantai Yang 《Journal of polymer science. Part A, Polymer chemistry》2007,45(3):500-508
A novel chiral N‐propargylsulfamide monomer ( 1a ) and its enantiomer ( 1b ) were synthesized and polymerized with (nbd)Rh+B?(C6H5)4 as a catalyst providing poly(1) (poly( 1a ) and poly( 1b )) in high yields (≥99%). Poly(1) could take stable helices in less polar solvents (chloroform and THF), demonstrated by strong circular dichroism signals and UV–vis absorption peaks at about 415 nm and the large specific rotations; but in more polar solvents including DMF and DMSO, poly(1) failed to form helix. Quantitative evaluation with anisotropy factor showed that the helical screw sense had a relatively high thermal stability. These results together with the IR spectra measured in solvents showed that hydrogen bonding between the neighboring sulfamide groups is one of the main driving forces for poly(1) to adopt stable helices. In addition, copolymerization of monomer 1a and monomer 2 was conducted, the solubility of poly(1) was improved drastically. However, the copolymerization had adverse effects on the formation of stable helices in the copolymers. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 500–508, 2007 相似文献
106.
Nikolai Yu. Bakaev 《BIT Numerical Mathematics》1998,38(3):462-485
We consider a Cauchy problem for the sectorial evolution equation with generally variable operator in a Banach space. Variable
stepsize discretizations of this problem by means of a strongly A(φ)-stable Runge-Kutta method are studied. The stability
and error estimates of the discrete solutions are derived for wider families of nonuniform grids than quasiuniform ones (in
particular, if the operator in question is constant or Lipschitz-continuous, for arbitrary grids). 相似文献
107.
Wojciech Bocian Jarosław Jaźwínski Lech Stefaniak Graham A. Webb 《Chemistry of Heterocyclic Compounds》1995,31(9):1103-1107
1H,13C,14N and15N NMR measurements are reported for four mesoionic 1-oxa-2, 3, 4-triazoles containing exocyclic nitrogenous groups. The NMR signal assignments are discussed and compared with those previously published for some corresponding oxatriazoles. The results obtained support the proposed cyclic mesoionic structures for the compounds studied. The questions of possible charge delocalization and valence tautomerism are addressed. Compound with N– H as a exocyclic group (Fig. 1) is found to be relatively unstable, this is attributed to proton migration in the corresponding non-cyclic form of this molecule.Published in Khimiya Geterotsikiicheskikh Soedinenii, No. 9, pp. 1260–1263, September, 1995. 相似文献
108.
Radu Ioan Boţ Ioan Bogdan Hodrea Gert Wanka 《Nonlinear Analysis: Theory, Methods & Applications》2007
Considering a constrained fractional programming problem, within the present paper we present some necessary and sufficient conditions, which ensure that the optimal objective value of the considered problem is greater than or equal to a given real constant. The desired results are obtained using the Fenchel–Lagrange duality approach applied to an optimization problem with convex or difference of convex (DC) objective functions and finitely many convex constraints. These are obtained from the initial fractional programming problem using an idea due to Dinkelbach. We also show that our general results encompass as special cases some recently obtained Farkas-type results. 相似文献
109.
Július Korbaš 《Topology and its Applications》2006,153(15):2976-2986
Our main result offers a new (quite systematic) way of deriving bounds for the cup-length of Poincaré spaces over fields; we outline a general research program based on this result. For the oriented Grassmann manifolds, already a limited realization of the program leads, in many cases, to the exact values of the cup-length and to interesting information on the Lyusternik-Shnirel'man category. 相似文献