全文获取类型
收费全文 | 10675篇 |
免费 | 1656篇 |
国内免费 | 514篇 |
专业分类
化学 | 1968篇 |
晶体学 | 47篇 |
力学 | 1919篇 |
综合类 | 195篇 |
数学 | 4956篇 |
物理学 | 3760篇 |
出版年
2024年 | 27篇 |
2023年 | 155篇 |
2022年 | 276篇 |
2021年 | 300篇 |
2020年 | 266篇 |
2019年 | 244篇 |
2018年 | 258篇 |
2017年 | 465篇 |
2016年 | 519篇 |
2015年 | 469篇 |
2014年 | 610篇 |
2013年 | 798篇 |
2012年 | 568篇 |
2011年 | 592篇 |
2010年 | 533篇 |
2009年 | 624篇 |
2008年 | 659篇 |
2007年 | 668篇 |
2006年 | 518篇 |
2005年 | 400篇 |
2004年 | 421篇 |
2003年 | 439篇 |
2002年 | 373篇 |
2001年 | 283篇 |
2000年 | 293篇 |
1999年 | 284篇 |
1998年 | 239篇 |
1997年 | 174篇 |
1996年 | 177篇 |
1995年 | 157篇 |
1994年 | 124篇 |
1993年 | 95篇 |
1992年 | 73篇 |
1991年 | 79篇 |
1990年 | 67篇 |
1989年 | 56篇 |
1988年 | 60篇 |
1987年 | 48篇 |
1986年 | 38篇 |
1985年 | 63篇 |
1984年 | 34篇 |
1983年 | 27篇 |
1982年 | 36篇 |
1981年 | 27篇 |
1980年 | 47篇 |
1979年 | 45篇 |
1978年 | 26篇 |
1977年 | 35篇 |
1976年 | 36篇 |
1974年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
81.
After the laser was invented in 1960, a phase conjugation mirror has been respected to be the most fantastic one for the laser
resonator composition because it can compensate any distortions of the laser beams occurred by the many inhomogenuities of
the laser media and optical components. Among the many phase conjugation configurations, the stimulated Brillouin scattering
phase conjugation mirror is the most simple one and many researchers have tried to utilize it to develop high power/energy
laser systems. For realizing a high energy/power laser system the thermal problem is the most difficult to solve, and some
researchers suggested a beam combination technique to reduce the thermal load of the big laser media to many small sized ones.
To accomplish the beam combination using stimulated Brillouin scattering phase conjugation mirrors (SBS-PCMs), it is necessary
to lock/control the phases of the SBS-PCMs. And some researchers have developed several ways for it, but they can lock the
phases of a limited number of beams overlapped at the foci less than 5, or lock the phases by back-seeding technique but it
loses the phase conjugation characteristics. For realization of the laser fusion driver, it is necessary to combine more than
10 or 100 beams. And the authors have developed recently a new phase controlling/locking technique which is isolated and independent
totally from other beams and it can be applied to an unlimited number of beams in principle. 相似文献
82.
83.
This paper considers an optimal boundary control problem fora hyperbolic system in which constant time lags appear in thestate equation and in the boundary condition simultaneously.Making use of Lion's scheme, necessary and sufficient conditionsof optimality for the Neumann problem are derived. 相似文献
84.
85.
We use the topological tool of Nielsen fixed-point theory to study the controllability of perturbed linear control processes whose control space can be reduced to a finite-dimensional one. These methods produce a lower bound on the number of controls that achieve a given target. We concentrate particularly on the case where the perturbation has sublinear growth, and we exhibit examples of multiple controls of various types that are detected by the Nielsen theory method.This research was partly supported by the Research Grant Teoria del Controllo dei Sistemi Dinamici, Ministero della Pubblica Istruzione, Roma, Italy. 相似文献
86.
In this paper, we identify a new class of stochastic linearconvex optimal control problems, whose solution can be obtained by solving appropriate equivalent deterministic optimal control problems. The term linear-convex is meant to imply that the dynamics is linear and the cost function is convex in the state variables, linear in the control variables, and separable. Moreover, some of the coefficients in the dynamics are allowed to be random and the expectations of the control variables are allowed to be constrained. For any stochastic linear-convex problem, the equivalent deterministic problem is obtained. Furthermore, it is shown that the optimal feedback policy of the stochastic problem is affine in its current state, where the affine transformation depends explicitly on the optimal solution of the equivalent deterministic problem in a simple way. The result is illustrated by its application to a simple stochastic inventory control problem.This research was supported in part by NSERC Grant A4617, by SSHRC Grant 410-83-0888, and by an INRIA Post-Doctoral Fellowship. 相似文献
87.
Summary A variety of bilipeptides has been synthesized and investigated by UV-VIS and CD spectroscopy to explore the conformational influence of peptide ligands on the covalently bound tetrapyrrol moiety. The results obtained are complemented by those reported previously. From the comprehensive data thus available several features of the peptidic chain regulating interactions with the bilatriene moiety have been elucidated. Accordingly, the presence of three amide linkages at the ligand is prerequiste for induction of pronounced conformational changes consisting either in a complete transition ofM intoP helical bilatriene species by inversion of all torsional angles, or in a stretching of the chromophore. The kind of conformational influence can be controlled by varying the position of the prolyl entity within a given peptide.Dedicated to Prof. Dr. Kurt Schaffner on occasion of his 60th birthday 相似文献
88.
Jerman S Podgornik A Cankar K Cadet N Skrt M Zel J Raspor P 《Journal of chromatography. A》2005,1065(1):107-113
The availability of sufficient quantities of DNA of adequate quality is crucial in polymerase chain reaction (PCR)-based methods for genetically modified food detection. In this work, the suitability of anion-exchange CIM (Convective Interaction Media; BIA Separations, Ljubljana, Slovenia) monolithic columns for isolation of DNA from food was studied. Maize and its derivates corn meal and thermally pretreated corn meal were chosen as model food. Two commercially available CIM disk columns were tested: DEAE (diethylaminoethyl) and QA (quaternary amine). Preliminary separations were performed with standard solution of salmon DNA at different pH values and different NaCl concentrations in mobile phase. DEAE groups and pH 8 were chosen for further isolations of DNA from a complex matrix-food extract. The quality and quantity of isolated DNA were tested on agarose gel electrophoresis, with UV-scanning spectrophotometry, and by amplification with real-time PCR. DNA isolated in this way was of suitable quality for further PCR analyses. The described method is also applicable for DNA isolation from processed foods with decreased DNA content. Furthermore, it is more effective and less time-consuming in comparison with the existing proposed methods for isolation of DNA from plant-derived foods. 相似文献
89.
90.
兴奋剂检测中的化学衍生化方法 总被引:1,自引:0,他引:1
本文评述了兴奋剂检测中的各种化学衍生化方法,对蛋白同化激素、麻醉镇痛剂、β-阻断剂和利尿剂分别进行了讨论。这四类药物结构各不相同,但绝大多数属于高沸点、难挥发的极性化合物,不适于直接进行GC或GC/MS分析。通过化学衍生化.不仅可增大试样的挥发性和稳定性,减小样品的极性,使原来难以进行GC分析的试样转变成适合于色谱分析的试样,而且通过衍生化还可达到改善分离效果、提高检测灵敏度的目的。 相似文献