全文获取类型
收费全文 | 7938篇 |
免费 | 359篇 |
国内免费 | 389篇 |
专业分类
化学 | 1411篇 |
晶体学 | 25篇 |
力学 | 187篇 |
综合类 | 32篇 |
数学 | 1510篇 |
物理学 | 1045篇 |
综合类 | 4476篇 |
出版年
2024年 | 11篇 |
2023年 | 51篇 |
2022年 | 64篇 |
2021年 | 96篇 |
2020年 | 105篇 |
2019年 | 114篇 |
2018年 | 111篇 |
2017年 | 147篇 |
2016年 | 124篇 |
2015年 | 157篇 |
2014年 | 323篇 |
2013年 | 403篇 |
2012年 | 364篇 |
2011年 | 461篇 |
2010年 | 363篇 |
2009年 | 478篇 |
2008年 | 469篇 |
2007年 | 571篇 |
2006年 | 552篇 |
2005年 | 449篇 |
2004年 | 413篇 |
2003年 | 397篇 |
2002年 | 345篇 |
2001年 | 349篇 |
2000年 | 285篇 |
1999年 | 217篇 |
1998年 | 187篇 |
1997年 | 140篇 |
1996年 | 116篇 |
1995年 | 100篇 |
1994年 | 96篇 |
1993年 | 82篇 |
1992年 | 74篇 |
1991年 | 72篇 |
1990年 | 50篇 |
1989年 | 55篇 |
1988年 | 56篇 |
1987年 | 38篇 |
1986年 | 26篇 |
1985年 | 20篇 |
1984年 | 26篇 |
1983年 | 12篇 |
1982年 | 23篇 |
1981年 | 14篇 |
1980年 | 24篇 |
1979年 | 24篇 |
1978年 | 8篇 |
1977年 | 10篇 |
1974年 | 3篇 |
1973年 | 4篇 |
排序方式: 共有8686条查询结果,搜索用时 46 毫秒
31.
We investigate the effects of adding uniformity requirements to concepts in computable structure theory such as computable categoricity (of a structure) and intrinsic computability (of a relation on a computable structure). We consider and compare two different notions of uniformity, previously studied by Kudinov and by Ventsov. We discuss some of their results and establish new ones, while also exploring the connections with the relative computable structure theory of Ash, Knight, Manasse, and Slaman and Chisholm and with previous work of Ash, Knight, and Slaman on uniformity in a general computable structure-theoretical setting. 相似文献
32.
用热传导方程控制激光辐照温度,建立了一种新回归方程以控制激光辐照硬化深度,选用卡尔丹公式列热传导方程及同归方程联立求解,可得到同时满足一定的硬化深度及表面最高温度双重要求的工艺参数,此种方法可作为激光硬化处理工艺参数的控制或预报,对本合金铸铁的激光硬化处理,其表面温度的下限应大于其熔点温度,即以表面产生微熔的快速冷凝处理为宜,并以选取低功率慢扫描为最佳。 相似文献
33.
Krzysztof Pawaowski 《K-Theory》1998,13(1):41-55
The paper presents a procedure for constructing smooth actions of finite perfect groups on spheres with fixed point sets having certain prescribed properties (Theorem A); in particular, having any prescribed configuration of Chern and Pontryagin numbers (Corollary C). The main ingredients used are equivariant thickening and equivariant surgery. 相似文献
34.
Hidetoshi Shimodaira 《Annals of the Institute of Statistical Mathematics》1997,49(3):395-410
The asymptotic error probability of Linhart's model selection test isevaluated, and compared with the nominal significance level. We examine thecase where the expected discrepancies of the candidate models from the truemodel are asymptotically equal. The local alternatives method is employed inthe limiting operation of the asymptotic evaluation. Although the errorprobability under the null hypothesis is actually shown to be equal to orless than the level for most situations, intolerable violations of the errorcontrol are observed for nested models: It is often erroneously concludedthat the smaller model is significantly better than the larger model. Toprevent this violation, a modification of Linhart's test statistic isproposed. The effectiveness of the proposed test is confirmed throughtheoretical analysis and numerical simulations. 相似文献
35.
Fusion-evaporation cross-sections for the α-induced reactions upon197Au,193Ir,191Ir,185Re,181Ta,121Sb and69Ga nuclei at bombarding energies near the Coulomb barrier have been measured by off-line observation of the γ-rays emitted
in the radioactive decay of the residual nuclei using stacked foil technique. The total fusion cross-section for the systems
have been compared with simple statistical model calculations using the code ALICE/91 as well as with the coupled channel
calculations that include the β2 and ν4 slatic deformations and dynamic couplings of the vibrational/rotational states of the target and the projet tile using the
code CCDEF. 相似文献
36.
廖业元 《北京交通大学学报(自然科学版)》1992,(1)
在用“奇偶点图上作业法”求解“中国邮路问题”时,需检查图中的每一个回路.当图中回路较多时,检查不便且易出错.针对此,本文建立了求解“中国邮路问题”的0-1规划模型,并给出了算例。 相似文献
37.
Structural characterisation of such bio-objects as fibrinogen solution, yeast cells, wheat seeds and bone tissues has been done using two versions of cryoporometry based on the integral Gibbs-Thomson (IGT) equation for freezing point depression of pore liquids and the measurements by 1H NMR spectroscopy (180-200 < T < 273 K) and the thermally stimulated depolarisation current (TSDC) method (90 < T < 273 K) of structured water. The IGT equation was solved using a self-consisting regularization procedure including the maximum entropy principle applied to the distribution function of pore size (PSD). Both methods give clear pictures of changes in the structural characteristics caused, e.g., by hydration and swelling of wheat seeds and yeast cells, coagulation and interaction of fibrinogen with solid nanoparticles in the aqueous media, and the human bone tissue disease. 相似文献
38.
The surgery obstruction of a normal map to a simple Poincaré pair (X, Y) lies in the relative surgery obstruction group L *(π 1(Y) → π 1(X)). A well-known result of Wall, the so-called π-π-theorem, states that in higher dimensions a normal map of a manifold with boundary to a simple Poincaré pair with π 1(X) ? π 1(Y) is normally bordant to a simple homotopy equivalence of pairs. In order to study normal maps to a manifold with a submanifold, Wall introduced the surgery obstruction groups LP * for manifold pairs and splitting obstruction groups LS *. In the present paper, we formulate and prove for manifold pairs with boundary results similar to the π-π-theorem. We give direct geometric proofs, which are based on the original statements of Wall’s results and apply obtained results to investigate surgery on filtered manifolds. 相似文献
39.
用三个关系式与Mathematica软件求第二类自然数幂和公式 总被引:1,自引:1,他引:0
首先介绍三个第二类自然数幂和关系式并对其中的两式给出证明,接着利用这些关系式与数学软件M athem atica4.0,给出求解第二类自然数幂和公式的若干机械计算方法. 相似文献
40.
Covering numbers of precompact symmetric convex subsets of Hilbert spaces are investigated. Lower bounds are derived for sets containing orthogonal subsets with norms of their elements converging to zero sufficiently slowly. When these sets are convex hulls of sets with power-type covering numbers, the bounds are tight. The arguments exploit properties of generalized Hadamard matrices. The results are illustrated by examples from machine learning, neurocomputing, and nonlinear approximation. 相似文献