全文获取类型
收费全文 | 88244篇 |
免费 | 8457篇 |
国内免费 | 7860篇 |
专业分类
化学 | 30267篇 |
晶体学 | 338篇 |
力学 | 8649篇 |
综合类 | 1778篇 |
数学 | 35011篇 |
物理学 | 28518篇 |
出版年
2023年 | 710篇 |
2022年 | 1575篇 |
2021年 | 1649篇 |
2020年 | 1750篇 |
2019年 | 1972篇 |
2018年 | 1715篇 |
2017年 | 2225篇 |
2016年 | 2533篇 |
2015年 | 2253篇 |
2014年 | 3421篇 |
2013年 | 5752篇 |
2012年 | 3764篇 |
2011年 | 4297篇 |
2010年 | 3768篇 |
2009年 | 5015篇 |
2008年 | 5602篇 |
2007年 | 5856篇 |
2006年 | 5261篇 |
2005年 | 4517篇 |
2004年 | 4213篇 |
2003年 | 4065篇 |
2002年 | 3773篇 |
2001年 | 3164篇 |
2000年 | 3027篇 |
1999年 | 2732篇 |
1998年 | 2525篇 |
1997年 | 2074篇 |
1996年 | 1866篇 |
1995年 | 1718篇 |
1994年 | 1498篇 |
1993年 | 1288篇 |
1992年 | 1211篇 |
1991年 | 1000篇 |
1990年 | 796篇 |
1989年 | 666篇 |
1988年 | 651篇 |
1987年 | 491篇 |
1986年 | 420篇 |
1985年 | 482篇 |
1984年 | 456篇 |
1983年 | 233篇 |
1982年 | 367篇 |
1981年 | 428篇 |
1980年 | 318篇 |
1979年 | 313篇 |
1978年 | 233篇 |
1977年 | 214篇 |
1976年 | 159篇 |
1974年 | 115篇 |
1973年 | 108篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
Yi Liu David D. Díaz Adrian A. Accurso K. Barry Sharpless Valery V. Fokin M. G. Finn 《Journal of polymer science. Part A, Polymer chemistry》2007,45(22):5182-5189
1,2,3‐Triazole‐based polymers generated from the Cu(I)‐catalyzed cycloaddition between multivalent azides and acetylenes are effective adhesive materials for metal surfaces. The adhesive capacities of candidate mixtures of azide and alkyne components were measured by a modified peel test, using a customized adhesive tester. A particularly effective tetravalent alkyne and trivalent azide combination was identified, giving exceptional strength that matches or exceeds the best commercial formulations. The addition of Cu catalyst was found to be important for the synthesis of stronger adhesive polymers when cured at room temperature. Heating also accelerated curing rates, but the maximum adhesive strengths achieved at both room temperature and high temperature were the same, suggesting that crosslinking reaches the same advanced point in all cases. Polytriazoles also form adhesives to aluminum, but copper is bound more effectively, presumably because active Cu(I) ions may be leached from the surface to promote crosslinking and adhesion. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5182–5189, 2007 相似文献
992.
Testing goodness of fit for the distribution of errors in multivariate linear models 总被引:2,自引:0,他引:2
M.D. Jimnez Gamero J. Muoz García R. Pino Mejías 《Journal of multivariate analysis》2005,95(2):301-322
In this paper, to test goodness of fit to any fixed distribution of errors in multivariate linear models, we consider a weighted integral of the squared modulus of the difference between the empirical characteristic function of the residuals and the characteristic function under the null hypothesis. We study the limiting behaviour of this test statistic under the null hypothesis and under alternatives. In the asymptotics, the rank of the design matrix is allowed to grow with the sample size. 相似文献
993.
Fabio Scardigli 《Foundations of Physics》2007,37(8):1278-1295
The Titius–Bode law for planetary distances is reviewed. A model describing the basic features of this rule in the “quantum-like”
language of a wave equation is proposed. Some considerations about the ’t Hooft idea on the quantum behavior of deterministic
systems with dissipation are discussed. 相似文献
994.
The propagation properties of decentered twisted Gaussian Schell-model (DTGSM) beams passing through a misaligned first-order optical system are studied. The explicit expressions for the cross-spectral density function and Wigner distribution function of the output beam are derived, which retain their form unchanged. It is shown that the DTGSM beams preserve their closed property. The second-order moments matrix and the Wigner distribution function evolve with the usual laws, whereas the first-order moments matrix varies, as if a ray passes through such system. The propagation of DTGSM beams through an aligned first-order optical system is treated as the limiting case that corresponds to the vanishing misalignment parameters. 相似文献
995.
We study elliptic systems of strongly nonlinear first-order differential equations in complex form on the plane. For such systems we develop the theory of Hilbert boundary value problems which is very much similar to the well-known theory for a holomorphic vector. Systems of nonlinear elliptic equations describe problems of interaction of several nonlinear stationary processes in the diffusive and convective mass and heat transport by hydrodynamic fluid flows. 相似文献
996.
The paper outlines a procedure to identify the space-and time-dependent external nonstationary load acting on a closed circular
cylindrical shell of medium thickness. Time-dependent deflections at several points of the shell are used as input data to
solve the inverse problem. Examples of numerical identification of various nonstationary loads, including moving ones are
presented. The relationship between the external load and the stress-strain state of the shell is described by the Volterra
equation of the first kind. The identification problem is solved using Tikhonov's regularization method and Apartsin's h-regularization method
__________
Translated from Prikladnaya Mekhanika, Vol. 44, No. 7, pp. 91–100, July 2008. 相似文献
997.
Reduction of tetranuclear heterometallic complex Mo2Mg2 was simulated using the B3LYP and PBE density functional methods. The results of geometry calculations of the initial complex
[MoVIO2Mg(MeOH)2(OMe)4]2 and a partially reduced MoV complex are in good agreement with experimental data. The reduced MoIII complex is characterized by a decrease in the binding energy of aqua ligands. Structural rearrangement of the complex with
release of a coordination position at the Mo atoms requires small energy expenditure. One can assume that the reduction of
the polynuclear complex causes overcrowding of its coordination sphere, which favors formation of dinitrogen complexes.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 441–457, March, 2008. 相似文献
998.
介绍了虚拟技术在实验教学改革中的作用与意义,探讨了电子信息系统实验教学改革的新思路与实现措施,并总结了实验教学改革的初步成果. 相似文献
999.
重力场与静电场特点的比较 总被引:2,自引:1,他引:1
“场”是一种客观存在的物质,但由于“场”具有不易直接感受的特殊存在形态,同学们对“场”的物质性的理解不够深刻,解决“场”的相关问题时也感到棘手.笔者就高中阶段最典型的两种场——“重力场”和“静电场”的力学性质与能量特点进行比较,使同学们对“场”的概念有更深刻的认识. 相似文献
1000.
聚乙二醇(PEG)6000经亚氨基二乙酸(IDA)修饰后和CuSO4反应,形成PEG修饰聚合物PEG-(IDA-Cu)2 ,与吐温80、磷酸盐混合,构成液-固亲和萃取体系,直接从大豆蛋白匀浆中提取氨基酸.选定萃取条件为磷酸盐摩尔比n(K2HPO4)∶n(NaH2PO4)为4.8∶1,体系pH值 7.70,总盐浓度为1.60 mol·L-1;吐温80的体积分数为10.5%.结果表明该体系对大豆蛋白匀浆中氨基酸的二次萃取率为66.5%,用离子交换技术后继处理,得纯度较高的组氨酸. 相似文献