全文获取类型
收费全文 | 478365篇 |
免费 | 4621篇 |
国内免费 | 1343篇 |
专业分类
化学 | 248085篇 |
晶体学 | 7838篇 |
力学 | 21627篇 |
综合类 | 16篇 |
数学 | 54566篇 |
物理学 | 152197篇 |
出版年
2021年 | 4117篇 |
2020年 | 4538篇 |
2019年 | 5098篇 |
2018年 | 6676篇 |
2017年 | 6923篇 |
2016年 | 9786篇 |
2015年 | 5712篇 |
2014年 | 9445篇 |
2013年 | 22452篇 |
2012年 | 17007篇 |
2011年 | 20440篇 |
2010年 | 14900篇 |
2009年 | 14820篇 |
2008年 | 18271篇 |
2007年 | 18121篇 |
2006年 | 16868篇 |
2005年 | 14859篇 |
2004年 | 13769篇 |
2003年 | 12319篇 |
2002年 | 12132篇 |
2001年 | 14433篇 |
2000年 | 10860篇 |
1999年 | 8398篇 |
1998年 | 6944篇 |
1997年 | 6772篇 |
1996年 | 6394篇 |
1995年 | 5715篇 |
1994年 | 5560篇 |
1993年 | 5284篇 |
1992年 | 6193篇 |
1991年 | 6313篇 |
1990年 | 6054篇 |
1989年 | 6043篇 |
1988年 | 5800篇 |
1987年 | 5917篇 |
1986年 | 5571篇 |
1985年 | 7129篇 |
1984年 | 7188篇 |
1983年 | 5854篇 |
1982年 | 6051篇 |
1981年 | 5865篇 |
1980年 | 5575篇 |
1979年 | 6113篇 |
1978年 | 6151篇 |
1977年 | 6247篇 |
1976年 | 6088篇 |
1975年 | 5665篇 |
1974年 | 5539篇 |
1973年 | 5581篇 |
1972年 | 3933篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
181.
A broad range echelle spectrograph with a CCD matrix detector is developed for different applications in atomic spectroscopy. The compact optical design in combination with a dispersive entrance slit illumination offers a low stray light level and high throughput in the UV spectral region comparable only with spectrographs of higher focal length. Ray tracing calculations for typical wavelengths and the multi-line spectrum of an iron arc show the excellent overall spectrum quality. The subtraction of two partial spectra of different steel alloys demonstrates the spectra evaluation possibilities of the CCD spectrograph. 相似文献
182.
On the basis of the invariant imbedding method the disturbance theory for complex constants of propagation is proposed. This approach allows us to consider the influence of layer and anisotropic fluctuations of refractive index on the beyond-the-horizon propagation in the adiabatic approximation with the existence of an evaporation duct. Finally, the authors consider some examples of the calculations and investigate stochastic effects connected with the interaction between fluctuating and regular waveguides. 相似文献
183.
The X-ray patterns for the nematic phase in a series of side-on fixed polysiloxanes show different kinds of diffuse elements which imply complex short range ordering. A systematic structural study of the evolution of the patterns versus two molecular parameters, namely the spacer length and the length of the terminal aliphatic tails, suggests the possible occurrence of a smectic C phase for certain values of these parameters. Taking into account these tendencies, new synthesis led to a nematic-smectic C polymorphism observed for the first time in side-on fixed polysiloxanes. 相似文献
184.
S. V. Chentsov 《Russian Physics Journal》1995,38(9):936-940
Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 79–83, September, 1995. 相似文献
185.
S. B. Vakarchuk 《Ukrainian Mathematical Journal》1996,48(4):601-606
In the spaces E q(Ω), 1 < q < ∞, introduced by Smirnov, we obtain exact order estimates of projective and spectral n-widths of the classes W r E p(Ω) and W r E p(Ω)Ф in the case where p and q are not equal. We also indicate extremal subspaces and operators for the approximative values under consideration. 相似文献
186.
A fast electrooptic modulation in a polymer waveguide using a ferroelectric liquid crystal has been proposed. In this device, the surface stabilized ferroelectric liquid crystal and the soft mode ferroelectric liquid crystal are used as an active material on the passive polymer waveguide, and electrooptic switching is realized by controlling the total reflection at the polymer waveguide-liquid crystal interface. The response time is of the order of several microseconds. The analogue electrooptic modulation in the waveguide is realized using the field induced linear molecular tilt of the electroclinic effect in the soft mode ferroelectric liquid crystal. 相似文献
187.
188.
S Barcza 《Journal of computer-aided molecular design》1991,5(6):509-510
Unlike in other branches of science and technology, computer programs and algorithms are generally not fully disclosed. This leads to duplication of effort, and prevents building new knowledge rapidly on existing knowledge. To remedy this, effective patents on computer programs and algorithms should be granted. The community of authors and inventors, along with expert advice from patent attorneys, have to arrive at effective and equitable definitions of obviousness and novelty, so that the boundaries of protection on one side, and free progress on the other, can be defined. The same reasons exist for patenting and disclosing computer software knowledge as for chemistry, electrical and mechanical inventions. Patenting has protected inventors and assured progress for many decades successfully in these fields. 相似文献
189.
190.
Thin films of polystyrene (PS), poly(methyl methacrylate) (PMMA) and polystyrene-polyacrylonitrile copolymer (PS-AN), containing various embedded transition-metal complexes, have been studied by FTIR microscopy. The spatial distributions of the transition-metal carbonyl complexes throughout the thin organic polymer films have been determined by a two-dimensional IR mapping procedure. The spectral variations observed in the distribution of the metal carbonyls throughout the different polymer films are discussed. The IR data show that the technique used to prepare the organometallic-embedded thin films (viz. freeze-drying of solutions followed by hot mechanical pressing of the residues) does in general lead to homogeneous films which may eventually find industrial application, e.g. as membrane sensors for small molecules. 相似文献