全文获取类型
收费全文 | 323049篇 |
免费 | 4543篇 |
国内免费 | 1116篇 |
专业分类
化学 | 177011篇 |
晶体学 | 4472篇 |
力学 | 13162篇 |
综合类 | 8篇 |
数学 | 38226篇 |
物理学 | 95829篇 |
出版年
2020年 | 2050篇 |
2019年 | 2032篇 |
2018年 | 2015篇 |
2017年 | 1906篇 |
2016年 | 4016篇 |
2015年 | 3381篇 |
2014年 | 4610篇 |
2013年 | 14309篇 |
2012年 | 10943篇 |
2011年 | 13573篇 |
2010年 | 8448篇 |
2009年 | 8442篇 |
2008年 | 12569篇 |
2007年 | 12805篇 |
2006年 | 12450篇 |
2005年 | 11383篇 |
2004年 | 10247篇 |
2003年 | 9065篇 |
2002年 | 8930篇 |
2001年 | 10278篇 |
2000年 | 7870篇 |
1999年 | 6224篇 |
1998年 | 4998篇 |
1997年 | 4852篇 |
1996年 | 4897篇 |
1995年 | 4470篇 |
1994年 | 4230篇 |
1993年 | 4074篇 |
1992年 | 4572篇 |
1991年 | 4405篇 |
1990年 | 4135篇 |
1989年 | 3955篇 |
1988年 | 4254篇 |
1987年 | 3908篇 |
1986年 | 3784篇 |
1985年 | 5521篇 |
1984年 | 5579篇 |
1983年 | 4499篇 |
1982年 | 4910篇 |
1981年 | 4940篇 |
1980年 | 4727篇 |
1979年 | 4839篇 |
1978年 | 4846篇 |
1977年 | 4857篇 |
1976年 | 4760篇 |
1975年 | 4657篇 |
1974年 | 4478篇 |
1973年 | 4695篇 |
1972年 | 2658篇 |
1971年 | 1968篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
111.
112.
113.
Matthew J. Katz 《Computational Geometry》1997,8(6):299-316
We present a new data structure for a set of n convex simply-shaped fat objects in the plane, and use it to obtain efficient and rather simple solutions to several problems including (i) vertical ray shooting—preprocess a set of n non-intersecting convex simply-shaped flat objects in 3-space, whose xy-projections are fat, for efficient vertical ray shooting queries, (ii) point enclosure—preprocess a set C of n convex simply-shaped fat objects in the plane, so that the k objects containing a query point p can be reported efficiently, (iii) bounded-size range searching— preprocess a set C of n convex fat polygons, so that the k objects intersecting a “not-too-large” query polygon can be reported efficiently, and (iv) bounded-size segment shooting—preprocess a set C as in (iii), so that the first object (if exists) hit by a “not-too-long” oriented query segment can be found efficiently. For the first three problems we construct data structures of size O(λs(n)log3n), where s is the maximum number of intersections between the boundaries of the (xy-projections) of any pair of objects, and λs(n) is the maximum length of (n, s) Davenport-Schinzel sequences. The data structure for the fourth problem is of size O(λs(n)log2n). The query time in the first problem is O(log4n), the query time in the second and third problems is O(log3n + klog2n), and the query time in the fourth problem is O(log3n).
We also present a simple algorithm for computing a depth order for a set as in (i), that is based on the solution to the vertical ray shooting problem. (A depth order for , if exists, is a linear order of , such that, if K1, K2 and K1 lies vertically above K2, then K1 precedes K2.) Unlike the algorithm of Agarwal et al. (1995) that might output a false order when a depth order does not exist, the new algorithm is able to determine whether such an order exists, and it is often more efficient in practical situations than the former algorithm. 相似文献
114.
A. J. Parsons S. D. J. Inglethorpe D. J. Morgan A. C. Dunham 《Journal of Thermal Analysis and Calorimetry》1997,48(1):49-62
Using a system based on non-dispersive infrared (NDIR) detectors, evolved gas analysis (EGA) was able to identify and quantify the principal volatiles produced by heating powdered samples of UK brick clays. From these results, atmospheric emissions likely to result from brick production can be predicted. In addition, EGA results for extruded brick clay test pieces are significantly different from those of powdered samples. Within an extruded brick clay body, evolved gases are contained within a pore system and evolved gas-solid phase reactions also occur. This EGA study provides further evidence on the nature of firing reactions within brick clay bodies. The qualitative and quantitative influence of heating rate — a key process condition in brick manufacture — on gas release is also outlined.Dedicated to Dr. Robert Mackenzie on the occasion of his 75th birthday 相似文献
115.
116.
117.
Whittum D.H. Ebihara K. Hiramatsu S. Kishiro J.-i. Monaka T. Ozaki T. Takayama K. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1993,21(1):136-141
Studies of microwave amplification with an in-focused electron beam drawn from an induction injector are reported. A free-electron laser (FEL) operating at 9.4 GHz and employing ion-focusing within the interaction region has achieved power in excess of 30 MW at 9.4 GHz, with a beam energy of 0.8 MeV and current of 0.7 kA. Peak gain is 20 dB/m, with no saturation after 15 wiggler periods. Also reported are the first evolution and detuning data for an ion-channel laser/maser (ICL). Two shortcomings of the prematurely halted ICL studies are poor frequency discrimination and a large axial plasma gradient. Prospects for operation with an upgraded 1.6 MeV accelerator are discussed 相似文献
118.
J. E. Fischer E. Werwa P. A. Heiney 《Applied Physics A: Materials Science & Processing》1993,56(3):193-196
We have used both reflection-geometry and grazing-incidence-geometry X-ray scattering to study thin films of C60 evaporated onto mica substrates via a hot-wall technique. The growth mode yields close-packed C60 planes, which are parallel to the substrate surface and which exhibit out-of-plane correlation lengths of 850 Å. In the film plane the C60 is at best pseudo-epitaxial, with a 0.9° distribution of crystallite orientations, a 450 Å in-plane correlation length, and a 3.7% lattice mismatch, better than obtained by other thin film techniques but far from the accepted definition of single crystal thin film epitaxy. 相似文献
119.
Chromatographia - A theoretical model is used to predict retention times of divalent metal cations in single-column ion chromatography using one or more ligands in the eluent. Stability constants... 相似文献
120.