全文获取类型
收费全文 | 6212篇 |
免费 | 115篇 |
国内免费 | 49篇 |
专业分类
化学 | 2160篇 |
晶体学 | 76篇 |
力学 | 290篇 |
数学 | 908篇 |
物理学 | 1200篇 |
无线电 | 1742篇 |
出版年
2020年 | 48篇 |
2016年 | 55篇 |
2015年 | 102篇 |
2014年 | 115篇 |
2013年 | 437篇 |
2012年 | 121篇 |
2011年 | 99篇 |
2010年 | 133篇 |
2009年 | 163篇 |
2008年 | 149篇 |
2007年 | 141篇 |
2006年 | 157篇 |
2005年 | 151篇 |
2004年 | 147篇 |
2003年 | 157篇 |
2002年 | 197篇 |
2001年 | 158篇 |
2000年 | 168篇 |
1999年 | 137篇 |
1998年 | 137篇 |
1997年 | 137篇 |
1996年 | 136篇 |
1995年 | 140篇 |
1994年 | 159篇 |
1993年 | 147篇 |
1992年 | 136篇 |
1991年 | 144篇 |
1990年 | 149篇 |
1989年 | 133篇 |
1988年 | 137篇 |
1987年 | 91篇 |
1986年 | 90篇 |
1985年 | 64篇 |
1984年 | 74篇 |
1983年 | 71篇 |
1982年 | 67篇 |
1981年 | 57篇 |
1980年 | 69篇 |
1979年 | 73篇 |
1978年 | 73篇 |
1977年 | 71篇 |
1976年 | 67篇 |
1975年 | 58篇 |
1974年 | 72篇 |
1973年 | 53篇 |
1972年 | 115篇 |
1971年 | 74篇 |
1970年 | 54篇 |
1969年 | 45篇 |
1968年 | 44篇 |
排序方式: 共有6376条查询结果,搜索用时 0 毫秒
91.
From postrecording interviews of professional singers, it was hypothesized that recording environments, i.e., sound-treated environment versus an auditorium, may induce different vocal behaviors. To test this hypothesis, three groups consisting of nonsingers, singers, and actors were recorded in two different recording environments: a sound-treated booth (IAC) and an auditorium (AUD). Three recordings were obtained from each participant: recording one (IAC) and two (AUD1) required the participants to read in a normal voice; recording three (AUD2) required participants to pretend that they were "performing" before a full house. Results indicated that only the singers and the actors exhibited significant spectral and/or frequency/duration differences from one recording environment to another, with the most dramatic differences exhibited by the singers. It was concluded that the environment in which we record experimental samples from professional voice users, especially singers, should be considered as a variable that can affect results. 相似文献
92.
93.
Let ${{\mathbb{Q}^4}(c)}$ be a four-dimensional space form of constant curvature c. In this paper we show that the infimum of the absolute value of the Gauss?CKronecker curvature of a complete minimal hypersurface in ${\mathbb{Q}^4(c), c\leq 0}$ , whose Ricci curvature is bounded from below, is equal to zero. Further, we study the connected minimal hypersurfaces M 3 of a space form ${{\mathbb{Q}^4}(c)}$ with constant Gauss?CKronecker curvature K. For the case c ?? 0, we prove, by a local argument, that if K is constant, then K must be equal to zero. We also present a classification of complete minimal hypersurfaces of ${\mathbb{Q}^4(c)}$ with K constant. 相似文献
94.
N. N. Bogolubov Jr A. V. Soldatov 《Proceedings of the Steklov Institute of Mathematics》2016,294(1):276-282
We show that a sequence of improving upper bounds to the ground state energy of the quantized Fröhlich polaron model can be obtained in a regular way by means of combining a variational method originated from the theory of coherent states with a generalized variational approach in quantum mechanics. Due to their variational nature, these bounds hold for arbitrary strength of the electron–phonon interaction. 相似文献
95.
A system of two initially entangled qubits interacting with a bosonic environment is considered. The interaction induces a loss of the initial entanglement of the two qubits, and for specific initial states it causes entanglement sudden death. An investigation of the modifications on the entanglement dynamics by a single pulse control field, performed in the two qubit system, shows that the control field can not only protect entangled states against sudden death but also induce a revival of entanglement in the two qubit system. 相似文献
96.
The authors follow up some previous work on the dynamics of pension funding by three notes. The first of these concerns contribution rates consisting of the normal cost plus a generalized amortization method for unfunded supplemental present value (actuarial accrued liability). The second note examines aggregate cost funding for active members when there exist consistent difference between the assumed and the actual rates of interest and of growth. The third note explores the operation of a variable annuity system in the context of our general model for pension funding dynamics. 相似文献
97.
In a multi-unit firm, such as a retail chain or a multi-plant manufacturer, we compare the business strategies developed by unit managers with the strategies that maximize corporate profit. The setting is one in which units face different markets and where learning spillovers between two units are enhanced if their strategies are more similar. When there is a small number of units, we find a tendency for managers' strategies to be excessively tailored to their local market. When the firm has many units, unit strategies can be either excessively or insufficiently standardized. 相似文献
98.
Eric L. McDowell Sam B. Nadler Jr. 《Proceedings of the American Mathematical Society》1996,124(4):1271-1276
The notion of an absolute fixed point set in the setting of continuum-valued maps will be defined and characterized.
99.
This paper constructs hyper-homology spectral sequences of Z-gradedand ROG-graded Mackey functors that compute Ext and Tor overG-equivariant S-algebras A ring spectra) for finite groups G.These specialize to universal coefficient and Künneth spectralsequences. 2000 Mathematics Subject Classification 55N91 (primary),55P43, 55U20, 55U25 (secondary). 相似文献
100.
Let H be a subgroup of a finite group G, and assume that p is a prime that does not divide |G : H|. In favorable circumstances, one can use transfer theory to deduce that the largest abelian p-groups that occur as factor groups of G and of H are isomorphic. When this happens, Tate’s theorem guarantees that the largest not-necessarily-abelian p-groups that occur as factor groups of G and H are isomorphic. Known proofs of Tate’s theorem involve cohomology or character theory, but in this paper, a new elementary
proof is given. It is also shown that the largest abelian p-factor group of G is always isomorphic to a direct factor of the largest abelian p-factor group of H.
Received: 17 June 2008 相似文献