全文获取类型
收费全文 | 77468篇 |
免费 | 23305篇 |
国内免费 | 18336篇 |
专业分类
化学 | 48755篇 |
晶体学 | 942篇 |
力学 | 5340篇 |
综合类 | 61篇 |
数学 | 10292篇 |
物理学 | 53719篇 |
出版年
2023年 | 658篇 |
2022年 | 641篇 |
2021年 | 536篇 |
2020年 | 789篇 |
2019年 | 1317篇 |
2018年 | 1308篇 |
2017年 | 1946篇 |
2016年 | 2048篇 |
2015年 | 2269篇 |
2014年 | 2079篇 |
2013年 | 3853篇 |
2012年 | 4129篇 |
2011年 | 6941篇 |
2010年 | 9746篇 |
2009年 | 9995篇 |
2008年 | 3215篇 |
2007年 | 2704篇 |
2006年 | 2422篇 |
2005年 | 2949篇 |
2004年 | 4277篇 |
2003年 | 3269篇 |
2002年 | 3065篇 |
2001年 | 3322篇 |
2000年 | 2367篇 |
1999年 | 2607篇 |
1998年 | 2246篇 |
1997年 | 1992篇 |
1996年 | 2322篇 |
1995年 | 2788篇 |
1994年 | 2814篇 |
1993年 | 3047篇 |
1992年 | 2679篇 |
1991年 | 2282篇 |
1990年 | 1950篇 |
1989年 | 2041篇 |
1988年 | 1874篇 |
1987年 | 1127篇 |
1986年 | 1199篇 |
1985年 | 860篇 |
1984年 | 980篇 |
1982年 | 895篇 |
1981年 | 730篇 |
1980年 | 769篇 |
1979年 | 528篇 |
1978年 | 531篇 |
1977年 | 636篇 |
1976年 | 1043篇 |
1973年 | 438篇 |
1972年 | 532篇 |
1971年 | 432篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
The dynamic behavior of the continuous biological reactor subject to product inhibition is analysed and classified in terms of multiplicity and stability of steady states and existence and stability character of limit cycles. Various boundary conditions are derived which delineate the parameter space into regions of dynamically different behavior. The predicted types of behavior are then illustrated by numerical computation of cells and product concentration trajectories. 相似文献
992.
Summary We report on the development of an adaptive optimum filter for processing the data of a resonant bar gravitational-wave detector.
This filter, based on the matched-filter theory, is adaptive in the sense that the function it realizes is derived from the
actual noise spectrum of the data being analysed (instead from an idealized model of the noise). Its implementation is mostly
based on frequency domain techniques. We also report on the application of the new filter to the data of the cryogenic antenna
Explorer of the Rome group, with particular reference to the comparison between its performance and that of an otpimum filter
with fixed values of the parameters. 相似文献
993.
The present paper covers three silabridged hafnocene dichlorides(1, 2 and 3) prepared by sequential reactions of α, ω-dichloropermethyl polysilane with cyclopentadienyl sodium, n-butyl lithium and hafnium tetrachloride. Their structures were characterized by elemental analyses, UV, 1H(13C) NMR and MS. Furthermore the crystal and molecular structures of 1 and 2 were determined by X-ray diffraction method. The crystal of 1 is monoclinic, space group C2/c with a=1. 3401(4), b=0. 9977(3), c = 1. 0922(4) nm; β=94. 07(1)° V=3. 6342 nm3, Z = 2, Dc = 2.155 g·cm-3. The final deviation factor R = 0. 064. The crystal of 2 is monoclinic, space group P21/c with a=0.0847(1), b=1.5181(1), c=2.9824(2) nm; β= 94. 07(1)°? V=3.634 nm3; Dc= l. 805 g·cm-3. The final deviation factor R = 0. 033. The relationship between the silabridged structure and spectral properties is also discussed. 相似文献
994.
From flash photolysis data of benzil and 2,2′-dichlorobenzil, the role of conformeric triplets in the formation of hydrogen
adduct radicals has been discussed. The planar relaxed triplet absorbing at 470 nm is less efficient in forming a hydrogen
adduct radical as compared to its puckered conformeric partner. Among the hydrogen donors, triethyl amine and isopropanol,
the former is more efficient in converting puckered triplets and less efficient in the case of planar conformers. Absorptions
of radicals and radical anions of 2,2′-dichlorobenzil appear at 355 nm and 460 nm respectively. These are blue-shifted as
compared to those of the parent compound benzil appearing at 370 nm and 540 nm, respectively. This blue-shift has been discussed
in terms of steric hindrance due to ortho-substitution. 相似文献
995.
996.
This paper presents a generalized Adadorov theory for anisotropic thin—walled beams. The theory takes account of the shear strain of the middle surface, which exerts a significant influence on the anisotropic thin-walled beams. A new approach is established to solve the governing equations, which have the same form for both open and closed section beams. The numerical examples show that the effects of the shear strain cannot be neglected for this class of beams.This work was part of research project supported by the National Natural Science Foundation of China 相似文献
997.
998.
In this paper,based on the results presented in part Ⅰ of this paper[18],we present a numerical embedding algorithm for solving the nonlinear complementarityproblem, and prove its convergence carefully. Numerical experiments show that thealgorithm is successful. 相似文献
999.
本文利用不连续罚函数方法将带有不等式约束的全局优化问题的求解转化为 讨论一非线性方程的求根问题,从而得到若干个全局最优性条件. 相似文献
1000.
PERSISTENCE AND GLOBAL STABILITY FOR TWO-SPECIES NONAUTONOMOUS PREDATOR-PREY SYSTEM WITH DIFFUSION AND TIME DELAY 总被引:3,自引:0,他引:3
In this paper, a non-autonomous predator-prey model with diffusion andcontinuous time delay is studied, where the prey can diffuse between two pat-ches of a heterogeneous environment with barriers between patches, but for thepredator, the diffusion does not involve a barrier between patches, further itis assumed that all the parameters are time-dependent. It is shown that thesystem can be made persistent under some appropriate conditions. Moreover,sufficient conditions that guarantee the existence of a unique periodic solutionwhich is globally asymptotic stable are derived. 相似文献