全文获取类型
收费全文 | 23022篇 |
免费 | 3348篇 |
国内免费 | 2454篇 |
专业分类
化学 | 16170篇 |
晶体学 | 277篇 |
力学 | 1364篇 |
综合类 | 188篇 |
数学 | 2301篇 |
物理学 | 8524篇 |
出版年
2024年 | 70篇 |
2023年 | 423篇 |
2022年 | 740篇 |
2021年 | 850篇 |
2020年 | 854篇 |
2019年 | 845篇 |
2018年 | 715篇 |
2017年 | 737篇 |
2016年 | 1021篇 |
2015年 | 1043篇 |
2014年 | 1177篇 |
2013年 | 1611篇 |
2012年 | 1869篇 |
2011年 | 1994篇 |
2010年 | 1299篇 |
2009年 | 1270篇 |
2008年 | 1465篇 |
2007年 | 1352篇 |
2006年 | 1220篇 |
2005年 | 972篇 |
2004年 | 775篇 |
2003年 | 659篇 |
2002年 | 633篇 |
2001年 | 464篇 |
2000年 | 458篇 |
1999年 | 485篇 |
1998年 | 423篇 |
1997年 | 425篇 |
1996年 | 468篇 |
1995年 | 366篇 |
1994年 | 383篇 |
1993年 | 277篇 |
1992年 | 256篇 |
1991年 | 240篇 |
1990年 | 172篇 |
1989年 | 131篇 |
1988年 | 119篇 |
1987年 | 98篇 |
1986年 | 95篇 |
1985年 | 86篇 |
1984年 | 59篇 |
1983年 | 49篇 |
1982年 | 38篇 |
1981年 | 28篇 |
1980年 | 31篇 |
1979年 | 18篇 |
1978年 | 10篇 |
1977年 | 8篇 |
1975年 | 7篇 |
1973年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
141.
142.
Y. -F. Lu M. Takai T. Nakata S. Nagatomo S. Namba 《Applied Physics A: Materials Science & Processing》1991,52(2):129-134
Maskless deposition of nickel lines on single crystalline Mn-Zn ferrite (MnO:ZnO:Fe2O3=31:17:52) has been investigated in a NiSO4 aqueous solution by Ar+ laser irradiation. A high deposition rate of up to 36.4m/s was achieved by a single scan of laser beam. The purity of deposited nickel layers is up to 86%. In particular, well-defined values of laser power and laser irradiation time were necessary for effective deposition. The deposition process was found to be a thermochemical process.On leave from D. S. Scanner Co., Ltd., 5-3-7. Fukushima, Osaka 553, Japan 相似文献
143.
144.
145.
We consider the following global optimization problems for a Lipschitz functionf implicitly defined on an interval [a, b]. Problem P: find a globally-optimal value off and a corresponding point; Problem Q: find a set of disjoint subintervals of [a, b] containing only points with a globally-optimal value and the union of which contains all globally optimal points. A two-phase algorithm is proposed for Problem P. In phase I, this algorithm obtains rapidly a solution which is often globally-optimal. Moreover, a sufficient condition onf for this to be the case is given. In phase II, the algorithm proves the-optimality of the solution obtained in phase I or finds a sequence of points of increasing value containing one with a globally-optimal value. The new algorithm is empirically compared (on twenty problems from the literature) with a best possible algorithm (for which the optimal value is assumed to be known), with a passive algorithm and with the algorithms of Evtushenko, Galperin, Shen and Zhu, Piyavskii, Timonov and Schoen. For small, the new algorithm requires only a few percent more function evaluations than the best possible one. An extended version of Piyavskii's algorithm is proposed for problem Q. A sufficient condition onf is given for the globally optimal points to be in one-to-one correspondance with the obtained intervals. This result is achieved for all twenty test problems.The research of the authors has been supported by AFOSR grants 0271 and 0066 to Rutgers University. Research of the second author has been also supported by NSERC grant GP0036426, FCAR grant 89EQ4144 and partially by AFOSR grant 0066. We thank Nicole Paradis for her help in drawing the figures. 相似文献
146.
We review here the results of our investigations concerning chaotic atomic scattering in the presence of a laser field. Particular emphasis is put on the existence of classical stable resonance structures, induced by the intense laser field, which are embedded in the field-free continuum. We show that phase space structures in the vicinity of a resonance island play an important role in the chaotic scattering behavior and form the basis for a mechanism to enhance the lifetimes of the collisional partners. Quantum calculations, based on a wave packet propagation method, show that quantum solutions are strongly influenced by the classical phase space structures. More specifically, a wave packet is found to spread differently in the regular and chaotic regions; in the latter case it spreads exponentially with time until saturation occurs, defining the saturation time. We also investigate the dependence of the spreading rates in both the regular and chaotic regimes. Calculations with an ensemble of classical trajectories are also presented to further illustrate the smoothing effects of varying. 相似文献
147.
148.
149.
Jian Ping LI* Ping LIU Yu Lu WANG College of Chemistry & Environmental Science Henan Normal University Xinxiang Key Laboratory of Environmental Science Technology of High Education of Henan Province Xinxiang 《中国化学快报》2003,14(7)
Azo compounds are widely utilized as analytic reagents and dyes1, they can also be used in material of non-linear optics, material of optics information storing in laser disks, and dyes with oil solubility in photochromy in modern technology2. Recently, many noteworthy studies have shown that some azo compounds possess excellent optical memory and photoelectric properties3,4. For example, polymer scaffolds bearing azobenzene-potential are useful for optical information storage, azo-dye doped… 相似文献
150.