全文获取类型
收费全文 | 41667篇 |
免费 | 2253篇 |
国内免费 | 3632篇 |
专业分类
化学 | 28931篇 |
晶体学 | 314篇 |
力学 | 580篇 |
综合类 | 685篇 |
数学 | 7713篇 |
物理学 | 9329篇 |
出版年
2023年 | 298篇 |
2022年 | 470篇 |
2021年 | 1543篇 |
2020年 | 821篇 |
2019年 | 922篇 |
2018年 | 648篇 |
2017年 | 769篇 |
2016年 | 937篇 |
2015年 | 986篇 |
2014年 | 1247篇 |
2013年 | 2530篇 |
2012年 | 1677篇 |
2011年 | 2002篇 |
2010年 | 1852篇 |
2009年 | 2434篇 |
2008年 | 2521篇 |
2007年 | 2627篇 |
2006年 | 2098篇 |
2005年 | 1475篇 |
2004年 | 1413篇 |
2003年 | 1341篇 |
2002年 | 3800篇 |
2001年 | 1437篇 |
2000年 | 1011篇 |
1999年 | 806篇 |
1998年 | 777篇 |
1997年 | 623篇 |
1996年 | 670篇 |
1995年 | 621篇 |
1994年 | 559篇 |
1993年 | 574篇 |
1992年 | 569篇 |
1991年 | 383篇 |
1990年 | 314篇 |
1989年 | 273篇 |
1988年 | 273篇 |
1987年 | 218篇 |
1986年 | 243篇 |
1985年 | 326篇 |
1984年 | 250篇 |
1983年 | 147篇 |
1982年 | 303篇 |
1981年 | 489篇 |
1980年 | 448篇 |
1979年 | 472篇 |
1978年 | 381篇 |
1977年 | 283篇 |
1976年 | 244篇 |
1974年 | 81篇 |
1973年 | 152篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
981.
We prove the existence of uncountably many nonisomorphic topological projective planes, each universal in the sense that it contains an isomorphic copy of every pseudoline arrangement. 相似文献
982.
Set-valued mappings from a topological space into subsets of a Banach space which satisfy a restricted form of weak upper semi-continuity, have particularly noteworthy properties. We establish a selection theorem for certain set-valued mappings from a (-) unfavourable topological space into subsets of a Banach space and as a consequence derive the property that restricted weak upper semi-continuous set-valued mappings which satisfy a minimality condition, from a (-) unfavourable topological space into subsets of a Banach space are single-valued and norm upper semi-continuous at the points of a residual subset of their domain. 相似文献
983.
Ayelet Lindenstrauss 《K-Theory》1996,10(3):239-265
Topological Hochschild homology is calculated for the rings /p[x]/(f(x)) (where p is prime and f(x) /p[x] any polynomial), [x]/(x
n) and [x]/(x
n–1). A spectral sequence argument is used for calculating the homology of the topological Hochschild homology spectrum, from which its stable homotopy structure can be read off since the spectrum is known for a priori reasons to be a restricted product of Eilenberg-MacLane spectra. 相似文献
984.
Qing Liu 《Transactions of the American Mathematical Society》1996,348(11):4577-4610
Let be a hyperelliptic curve of genus over a discrete valuation field . In this article we study the models of over the ring of integers of . To each Weierstrass model (that is a projective model arising from a hyperelliptic equation of with integral coefficients), one can associate a (valuation of) discriminant. Then we give a criterion for a Weierstrass model to have minimal discriminant. We show also that in the most cases, the minimal regular model of over dominates every minimal Weierstrass model. Some classical facts concerning Weierstrass models over of elliptic curves are generalized to hyperelliptic curves, and some others are proved in this new setting.
985.
Spectrophotometric methods for the determination of labetalol hydrochloride in pure and dosage forms
Simple and sensitive Spectrophotometric methods for the determination of labetalol hydrochloride are described. The first two are based on the oxidative coupling reaction of labetalol hydrochloride withp-N,N-dimethyl-phenylenediamine dihydrochloride (method A, max 685 nm) and 3-methyl-2-benzothiazolinone hydrazone hydrochloride (method B, max 545 nm) in the presence of sodium hypochlorite and eerie ammonium sulphate as oxidants, respectively. The third depends on the formation of an ion-association complex of labetalol hydrochloride with suprachen violet 3B at pH 1.3, which is extracted into chloroform (method C, max 565 nm). The methods obey Beer's law and the precision and accuracy of the methods were checked against the B.P. reference method and the relative standard deviations were in the range 0.35–0.52%. These methods are applied to the determination of labetalol in dosage forms. 相似文献
986.
Mattia Falconi Ruggero Gallimbeni Emanuele Paci 《Journal of computer-aided molecular design》1996,10(5):490-498
Summary Molecular dynamics (MD) simulations of 100 ps have been carried out to study the active-site behaviour of the Cu,Zn superoxide dismutase dimer (SOD) in water. The active site of each subunit was monitored during the whole simulation by calculating the distances between functional residues and the catalytic copper. The results indicate that charge orientation is maintained at each active site but the solvent accessibility varies. Analysis of the MD simulation, carried out by using the atomic displacement covariance matrix, has shown a different intra-subunit correlation pattern for the two monomers and the presence of inter-subunit correlations. The MD simulation presented here indicates an asymmetry in the two active sites and different dynamic behaviour of the two SOD subunits. 相似文献
987.
Thermal solid-phase decomposition of anhydrous copper(ii) formate has been studied at 120–180 ° The rate of gas evolution during the decomposition depends on the depth of conversion and can be presented as the sum of first-order reaction rates and the rate of the autocatalytic process (a second-order reaction). The evolution of the solid phase during thermolysis has been observed by optical microscopy. The decomposition of copper formate is a complex topochemical process, a combination of homogeneous and heterogeneous transformations and dispersion of large crystals.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. l, pp. 72–76, January, 1996. 相似文献
988.
Mamoru Sato Yukiteru Katsube Masaaki Katai Jun' ichi Katakawa Tadahiro Tetsumi 《Journal of chemical crystallography》1996,26(2):153-156
The crystal and molecular structure of a grayanotoxin III derivative, 6-0-acetylgrayanotoxin III is presented. The crystal is orthorhombic, space group P212121, witha=15.582(3),b=21.304(3),c=6.339(3)Å,V=2104(1) Å3
Z=4. The structure was solved by direct methods and refined by full matrix least-squares methods to a finalR=0.047 for 1763 independent reflections withF
0>3 (F
0) The molecule is based on a tetracyclic structure consisting of two five-membered, one six-membered, and one seven-membered ring with various conformations. 相似文献
989.
Summary A thin layer chromatographic method for a qualitative screening-test and a quantitative analysis of 2,4,6-TNT, biodegradation products, octogen and hexogen in ammunition wastes was developed using both polar and non-polar modified sorbents. For enrichment a solidphase extraction on LiChrolut® EN followed by removal with methanol/acetonitrile (11 v/v) was chosen. To imitate real samples, spiked tap water samples of known composition were used. 相似文献
990.
R. Balasubramanian M. Langevin T. N. Shorey M. Waldschmidt 《Monatshefte für Mathematik》1996,121(4):295-307
In this paper we consider an analogue of the problem of Erds and Woods for arithmetic progressions. A positive answer follows from theabc conjecture. Partial results are obtained unconditionally. 相似文献