全文获取类型
收费全文 | 7892篇 |
免费 | 614篇 |
国内免费 | 1041篇 |
专业分类
化学 | 2854篇 |
晶体学 | 26篇 |
力学 | 510篇 |
综合类 | 113篇 |
数学 | 4853篇 |
物理学 | 1191篇 |
出版年
2024年 | 11篇 |
2023年 | 85篇 |
2022年 | 102篇 |
2021年 | 166篇 |
2020年 | 196篇 |
2019年 | 212篇 |
2018年 | 197篇 |
2017年 | 223篇 |
2016年 | 252篇 |
2015年 | 217篇 |
2014年 | 347篇 |
2013年 | 689篇 |
2012年 | 334篇 |
2011年 | 405篇 |
2010年 | 346篇 |
2009年 | 504篇 |
2008年 | 544篇 |
2007年 | 549篇 |
2006年 | 512篇 |
2005年 | 419篇 |
2004年 | 378篇 |
2003年 | 370篇 |
2002年 | 354篇 |
2001年 | 296篇 |
2000年 | 302篇 |
1999年 | 199篇 |
1998年 | 209篇 |
1997年 | 182篇 |
1996年 | 163篇 |
1995年 | 142篇 |
1994年 | 117篇 |
1993年 | 82篇 |
1992年 | 74篇 |
1991年 | 57篇 |
1990年 | 43篇 |
1989年 | 25篇 |
1988年 | 35篇 |
1987年 | 31篇 |
1986年 | 24篇 |
1985年 | 30篇 |
1984年 | 28篇 |
1983年 | 9篇 |
1982年 | 7篇 |
1981年 | 9篇 |
1980年 | 16篇 |
1979年 | 14篇 |
1978年 | 13篇 |
1977年 | 6篇 |
1976年 | 9篇 |
1973年 | 3篇 |
排序方式: 共有9547条查询结果,搜索用时 31 毫秒
1.
2.
《Indagationes Mathematicae》2021,32(6):1229-1239
3.
Most notable Kinetoplastids are of the genus Trypanosoma and Leishmania, affecting several millions of humans in Africa and Latin America. Current therapeutic options are limited by several drawbacks, hence the need to develop more efficacious inhibitors. An investigation to decipher the mechanism behind greater inhibitory potency of a chroman-4-one derivative (compound 1) in Trypanosoma brucei pteridine reductase 1 (TbPTR1) and Leishmania major pteridine reductase 1 (LmPTR1) was performed. Estimation of ΔGbind revealed that compound 1 had a greater binding affinity in TbPTR1 with a ΔGbind value of −49.0507 Kcal/mol than −29.2292 Kcal/mol in LmPTR1. The ΔGbind in TbPTR1 were predominantly contributed by “strong” electrostatic energy compared to the “weak” van der Waals in LmPTR1. In addition to this, the NADPH cofactor contributed significantly to the total energy of TbPTR1. A characteristic weak aromatic π interaction common in PTR1 was more prominent in TbPTR1 than LmPTR1. The consistent occurrence of high-affinity conventional hydrogen bond interactions as well as a steady interaction of crucial active site residues like Arg14/Arg17, Ser95/Ser111, Phe97/Phe113 in TbPTR1/LmPTR1 with chroman-4-one moiety equally revealed the important role the moiety played in the activity of compound 1. Overall, the structural and conformational analysis of the active site residues in TbPTR1 revealed them to be more rigid than LmPTR1. This could be the mechanism of interaction TbPTR1 employs in exerting a greater potency than LmPTR1. These findings will further give insight that will be assistive in modifying compound 1 for better potency and the design of novel inhibitors of PTR1. 相似文献
4.
An M/G/1 retrial queueing system with additional phase of service and possible preemptive resume service discipline is considered. For an arbitrarily distributed retrial time distribution, the necessary and sufficient condition for the system stability is obtained, assuming that only the customer at the head of the orbit has priority access to the server. The steady-state distributions of the server state and the number of customers in the orbit are obtained along with other performance measures. The effects of various parameters on the system performance are analysed numerically. A general decomposition law for this retrial queueing system is established. 相似文献
5.
This paper deals mainly with generalizations of results in finitary combinatorics to infinite ordinals. It is well-known that for finite ordinals ∑bT<αβ is the number of 2-element subsets of an α-element set. It is shown here that for any well-ordered set of arbitrary infinite order type α, ∑bT<αβ is the ordinal of the set M of 2-element subsets, where M is ordered in some natural way. The result is then extended to evaluating the ordinal of the set of all n-element subsets for each natural number n ≥ 2. Moreover, series ∑β<αf(β) are investigated and evaluated, where α is a limit ordinal and the function f belongs to a certain class of functions containing polynomials with natural number coefficients. The tools developed for this result can be extended to cover all infinite α, but the case of finite α appears to be quite problematic. 相似文献
6.
Elena Kardash-Strochkova Yakov I. Tur’yan I. Kuselman Naphtali Brodsky 《Accreditation and quality assurance》2002,7(6):250-254
The results of two interlaboratory comparisons of acid number determinations in used motor oils are discussed. It is shown
that the comparability of the measurement results is not as good as that required by known standards for petroleum products.
The problem is motor oil contaminants which accumulated during use, and which are the source of a matrix effect in the acid
number determination. The standard methods’ drawbacks are analyzed and some improvements are proposed. Repeatability and accuracy
of the improved methods are evaluated.
Received: 11 December 2001 Accepted: 15 February 2002 相似文献
7.
Taekyun Kim 《Journal of Mathematical Analysis and Applications》2002,273(1):236-242
The purpose of this paper is to give a proof of Kummer type congruence for the q-Bernoulli numbers of higher order, which is an answer to a part of the problem in a previous publication (see Indian J. Pure Appl. Math. 32 (2001) 1565-1570). 相似文献
8.
Mariano J. Valderrama 《商业与工业应用随机模型》1991,7(1):93-106
Alternative procedures for representing a stochastic signal as a denumerable series with uncorrelated terms are developed. The study includes considerations about parametric rescaling and its repercussions on the orthogonal expansion, as well as numerical techniques for approaching such an expansion. In addition, applications to the Gaussian characterization of stochastic signals, filtering and stochastic modelling are treated. 相似文献
9.
《组合设计杂志》2002,10(5):283-293
An Orthogonal Double Cover (ODC) of the complete graph Kn by an almost‐hamiltonian cycle is a decomposition of 2Kn into cycles of length n?1 such that the intersection of any two of them is exactly one edge. We introduce a new class of such decompositions. If n is a prime, the special structure of such a decomposition allows to expand it to an ODC of Kn+1 by an almost‐hamiltonian cycle. This yields the existence of an ODC of Kp+1 by an almost‐hamiltonian cycle for primes p of order 3 mod 4 and its eventual existence for arbitrary primes p. © 2002 Wiley Periodicals, Inc. J Combin Designs 10: 283–293, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/jcd.10011 相似文献
10.
This paper gives some global and uniform convergence estimates for a class of subspace correction (based on space decomposition) iterative methods applied to some unconstrained convex optimization problems. Some multigrid and domain decomposition methods are also discussed as special examples for solving some nonlinear elliptic boundary value problems.