全文获取类型
收费全文 | 155083篇 |
免费 | 17118篇 |
国内免费 | 17782篇 |
专业分类
化学 | 90834篇 |
晶体学 | 4440篇 |
力学 | 12971篇 |
综合类 | 1794篇 |
数学 | 27306篇 |
物理学 | 52638篇 |
出版年
2024年 | 195篇 |
2023年 | 1336篇 |
2022年 | 2216篇 |
2021年 | 4207篇 |
2020年 | 4120篇 |
2019年 | 3885篇 |
2018年 | 3476篇 |
2017年 | 4513篇 |
2016年 | 5522篇 |
2015年 | 4976篇 |
2014年 | 6958篇 |
2013年 | 11700篇 |
2012年 | 9671篇 |
2011年 | 9733篇 |
2010年 | 8335篇 |
2009年 | 9920篇 |
2008年 | 10093篇 |
2007年 | 10299篇 |
2006年 | 9141篇 |
2005年 | 7830篇 |
2004年 | 7262篇 |
2003年 | 6494篇 |
2002年 | 8451篇 |
2001年 | 5036篇 |
2000年 | 4475篇 |
1999年 | 3807篇 |
1998年 | 3444篇 |
1997年 | 2759篇 |
1996年 | 2395篇 |
1995年 | 2261篇 |
1994年 | 2115篇 |
1993年 | 1750篇 |
1992年 | 1773篇 |
1991年 | 1214篇 |
1990年 | 912篇 |
1989年 | 775篇 |
1988年 | 749篇 |
1987年 | 555篇 |
1986年 | 483篇 |
1985年 | 612篇 |
1984年 | 516篇 |
1983年 | 262篇 |
1982年 | 465篇 |
1981年 | 610篇 |
1980年 | 526篇 |
1979年 | 557篇 |
1978年 | 435篇 |
1977年 | 342篇 |
1976年 | 270篇 |
1973年 | 184篇 |
排序方式: 共有10000条查询结果,搜索用时 555 毫秒
941.
Abakumov G. A. Druzhkov N. O. Kurskii Yu. A. Shavyrin A. S. 《Russian Chemical Bulletin》2003,52(3):712-717
Products of thermal transformation of substituted N-aryl-o-quinoneimines were studied using NMR spectroscopy. The formation of 4aH-phenoxazine, which was further dimerized by the Diels—Alder reaction, was established. 相似文献
942.
Hossam A. Zaki 《Computational Optimization and Applications》1995,4(1):23-45
State-of-the-art computational results have shown that the shortest augmenting path (SAP) methods are more efficient than other primal-dual and primal-simplex based methods for solving the linear assignment problem on uniprocessor computers. There is, however, some controversy concerning their merits when compared with Bertsekas' auction algorithm on multiprocessor computers. In this study we investigate the performance of these competing methods on the Alliant FX/8. For each method, theoretical motivation, sources of parallelism and computational results are presented. 相似文献
943.
Transfer matrix approach of vibration isolation analysis of periodic composite structure 总被引:1,自引:0,他引:1
Wang Yong Huang Qibai Zhou Minggang Xu Zhisheng 《Archive of Applied Mechanics (Ingenieur Archiv)》2007,77(7):461-471
The transmission properties of elastic waves propagating in a three-dimensional composite structure embedded periodically
with spherical inclusions are analyzed by the transfer matrix method in this paper. Firstly, the periodic composite structures
are divided into many layers, the transfer matrix of monolayer structure is deduced by the wave equations, and the transfer
matrix of the entire structure is obtained in the case of boundary conditions of displacement and stress continuity between
layers. Then, the effective impedance of the structure is analyzed to calculate its reflectivity and transmissivity of vibration
isolation. Finally, numerical simulation is carried out; the experiment results validate the accuracy and feasibility of the
method adopted in the paper and some useful conclusions are obtained.
Project (No. 50075029) supported by the National Natural Science Foundation of China. 相似文献
944.
Attapol Kaewkhao 《Journal of Mathematical Analysis and Applications》2007,333(2):950-958
We give some sufficient conditions for the Domínguez-Lorenzo condition in terms of the James constant, the Jordan-von Neumann constant, and the coefficient of weak orthogonality. As a consequence, we obtain fixed point theorems for multivalued nonexpansive mappings. 相似文献
945.
Direct Shooting Method for the Numerical Solution of Higher-Index DAE Optimal Control Problems 总被引:3,自引:0,他引:3
A method for the numerical solution of state-constrained optimal control problems subject to higher-index differential-algebraic equation (DAE) systems is introduced. For a broad and important class of DAE systems (semiexplicit systems with algebraic variables of different index), a direct multiple shooting method is developed. The multiple shooting method is based on the discretization of the optimal control problem and its transformation into a finite-dimensional nonlinear programming problem (NLP). Special attention is turned to the mandatory calculation of consistent initial values at the multiple shooting nodes within the iterative solution process of (NLP). Two different methods are proposed. The projection method guarantees consistency within each iteration, whereas the relaxation method achieves consistency only at an optimal solution. An illustrative example completes this article. 相似文献
946.
有限维路代数的K_1群 总被引:1,自引:0,他引:1
本文通过计算有限维路代数k△的单位群和单位群的阿贝尔化,完全刻划了 任意域上有限维路代数的K1群. 相似文献
947.
在(NH4)3VS4/CuI/Py反应体系中合成了新化合物 [VS4Cu6(Py)8I3]并测定其晶体结构。该化合物(C40H40N8Cu6I3S4V)属正交晶系, 空间群为Fdd2, 晶胞参数为: a = 29.924(6), b = 13.475(3), c = 25.853(5) , V = 10425(4) ?, Dc = 2.006 g/cm3, Mr = 1573.92, Z = 8, (MoK) = 4.546 mm-1, F(000) = 6048。结构由直接法解出, 用全矩阵最小二乘法修正, 最终偏离因子R = 0.023, wR = 0.069。簇合物分子是由6个带端基配体的Cu沿着四面体单元VS4的6条SS边配位而成, 6个Cu排列成了1个八面体, V基本位于八面体的中心, 整个分子具有C2对称性。 相似文献
948.
949.
§ 1 IntroductionConsiderthefollowingnonlinearoptimizationproblem :minimizef(x)subjecttoC(x) =0 , a≤x≤b ,( 1 .1 )wheref(x) :Rn→R ,C(x) =(c1(x) ,c2 (x) ,...,cm(x) ) T:Rn→Rm aretwicecontinuouslydifferentiable,m≤n ,a ,b∈Rn.Trustregionalgorithmsareveryeffectiveforsolvingnonlinearoptimi… 相似文献
950.
Dichang Zhang 《Journal of Thermal Analysis and Calorimetry》1995,45(1-2):141-150
A cracking catalyst designatedSRNY was manufactured from a commercialSRNY molecular sieve (M.S.). The support consisted of kaolin, clay and SiO2. The coking behaviour of theSRNY M.S., the support and the catalyst were examined with light diesel oil (LDO) as feedstock in a microreactor. The physico-chemical properties of both fresh and aged samples, subjected to or not subjected to the cracking reaction ofLDO, were sequentially characterized by means of pore structure determination and thermal analysis. The pore structure included the specific surface area and the pore volume or porosity. Thermal analysis methods used included TG and DSC. The results indicated that all coked samples exhibited obvious changes in surface pore structure and acidity in comparison with non-coked samples. Their specific surface area and acid amount decreased with increase in the coke content of the samples. The apparent activation energy data obtained from decoking samples in an air flow, using the temperature-programmed oxidation (TPO) method, showed that the kinetic parameters of theSRNY M.S. differed from those of theSRNY catalyst and its support. 相似文献