全文获取类型
收费全文 | 31714篇 |
免费 | 5444篇 |
国内免费 | 2675篇 |
专业分类
化学 | 15262篇 |
晶体学 | 544篇 |
力学 | 919篇 |
综合类 | 201篇 |
数学 | 930篇 |
物理学 | 10672篇 |
无线电 | 11305篇 |
出版年
2024年 | 73篇 |
2023年 | 332篇 |
2022年 | 550篇 |
2021年 | 672篇 |
2020年 | 933篇 |
2019年 | 844篇 |
2018年 | 900篇 |
2017年 | 1099篇 |
2016年 | 1338篇 |
2015年 | 1424篇 |
2014年 | 1706篇 |
2013年 | 2860篇 |
2012年 | 2128篇 |
2011年 | 2139篇 |
2010年 | 1724篇 |
2009年 | 1779篇 |
2008年 | 1968篇 |
2007年 | 2020篇 |
2006年 | 1842篇 |
2005年 | 1668篇 |
2004年 | 1509篇 |
2003年 | 1377篇 |
2002年 | 1315篇 |
2001年 | 1004篇 |
2000年 | 985篇 |
1999年 | 791篇 |
1998年 | 740篇 |
1997年 | 579篇 |
1996年 | 524篇 |
1995年 | 552篇 |
1994年 | 425篇 |
1993年 | 339篇 |
1992年 | 307篇 |
1991年 | 230篇 |
1990年 | 182篇 |
1989年 | 129篇 |
1988年 | 131篇 |
1987年 | 117篇 |
1986年 | 110篇 |
1985年 | 91篇 |
1984年 | 88篇 |
1983年 | 43篇 |
1982年 | 59篇 |
1981年 | 47篇 |
1980年 | 38篇 |
1979年 | 42篇 |
1978年 | 17篇 |
1977年 | 13篇 |
1975年 | 8篇 |
1973年 | 16篇 |
排序方式: 共有10000条查询结果,搜索用时 301 毫秒
91.
Peptides containing azaglycine located terminally or within the backbone have been prepared in the solid phase by means of an automatic synthesizer. 相似文献
92.
一种铁氧体移相驱动器专用集成电路 总被引:1,自引:1,他引:0
介绍了SA018铁氧体移相驱动器专用集成电路的工作原理,电路设计和实验结果。该电路的内部电路设计有双路激励驱动器,放大器,积分器和双路高速比较器等功能单元。将铁氧体移相器的激励驱动器和相位控制器融于一体,大大减少了铁氧体移相器的外围设计。 相似文献
93.
Benjamin S. Hsiao Rong-Ming Ho Stephen Z. D. Cheng 《Journal of Polymer Science.Polymer Physics》1995,33(17):2439-2447
Unique crystallization and melting behavior in poly(aryl ether ketone ketone) containing alternated terephthalic and isophthalic moieties were studied by time-resolved synchrotron x-ray methods. Recently, this material has been shown to exhibit three polymorphs (forms I, II, and III). In this work, we further investigated their distinctive thermal properties and found that form I is the dominating and the most thermally stable phase while form II is favored by fast nucleation conditions and is the least stable phase. On the other hand, form III represents a minor intermediate phase that usually coexists with form I and can be transferred from form II and to form I. Structural and morphological changes in form I have been followed by simultaneous wide-angle x-ray diffraction (WAXD)/small-angle x-ray scattering (SAXS) measurements during cold- or melt-crystallization and subsequent melting. In all cases, a larger dimensional change was found in the crystallographic a-axis than the b-axis during heating and cooling. This may be due to the greater lateral stress variation with respect to temperature along the a direction of the primary lamellae which is induced by either the formation of secondary lamellae or the preferential chain-folding direction in poly(aryl ether ketone ketone)s. During the phase transitions of form II ← III in the cold-crystallized specimen and form III ← I in the melt-crystallized samples, lamellar variables (long period, lamellar thickness, and invariant) obtained from SAXS remain almost constant. This indicates that the density distribution in the long spacing is independent of the melting in form II or III. For melt-crystallization, the corresponding changes in unit-cell dimensions and lamellar morphology during the annealing-induced low endotherm are most consistent with the argument that these changes are due to the melting of thin lamellar population. © 1995 John Wiley & Sons, Inc. 相似文献
94.
D. V. Kazakov A. I. Voloshin N. N. Kabal'nova V. V. Shereshovets V. P. Kazakov 《Russian Chemical Bulletin》1996,45(10):2452-2453
Chemiluminescence (CL) was found upon the isomerization of dimethyldioxirane in the gas phase under argon atmosphere. The intensity of CL increases as temperature increases and decreases with time at constant temperature. If Silipor is placed in a cell containing the dimethyldioxirane vapor in argon, the intensity of CL sharply increases (more than 10 times) and then decreases following the exponential law. In all cases tripletly excited methyl acetate is the emitter of chemiluminescence.[/ p]Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2582–2583, October 1996. 相似文献
95.
A method employing a wide pore polymeric reversed phase column has been developed for the separation of most of the chlorophylls and related compounds previously described as occurring in marine microalgae. The high selectivity toward molecular shape of this kind of stationary phase has enabled compounds of very similar structure, such as chlorophylls c1, c2 and Mg-divinylpheoporphyrin a5 monomethyl ester, and chlorophyll a and the phytol-substituted chlorophyll c-like pigments, which commonly coelute on monomeric bonded phases, to be resolved in a single run. Some of these pigments, formerly thought to be a single compound, have, in fact, been demonstrated to be groups of two or more. The method has been successfully applied to both algal cultures and natural sea water samples. When visible light absorbance detection was used, the method proved suitable for separation of various carotenoids. 相似文献
96.
激光相位成像雷达的研究 总被引:1,自引:0,他引:1
利用无合作目标漫反射激光相位测距的原理,对关键单元技术进行分析和设计,研制成一种用于自主式车辆视觉导引的激光相位成像雷达的原理样机. 相似文献
97.
98.
The equivalent geometrical configurations of linear ordered orthogonal arrays are determined when their strengths are 3 and 4. Existence of such geometrical configurations is investigated. They are also useful in the study of (T, M, S)-nets. 相似文献
99.
本文将等效介电常数近似分析方法在应用范围和处理方法上进行了一些改进.发展为双等效介电常数近似分析法,然后用它来分析矩形介质波导阵列.推得两个一维周期的耦合特征方程。如果将Macatili方法应用范围扩展用来研究该波导阵列也会得到同样的结果,它们都能在二维平面上较准确地反应出通带和阻带等主要周期特性。 相似文献
100.
W. Kockelmann M. Hofmann O. Moze S.J. Kennedy K.H.J. Buschow 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,30(1):25-32
The element distributions and the magnetic ordering behaviour of compounds RNi10Si2 (R
=
Tb, Dy, Ho, Er, Tm) have been studied by neutron powder diffraction down to temperatures of 1.6 K. The compounds crystallize
in an ordered variant of the ThMn12 structure type in the tetragonal space group P4/nmm. An ordered 1:1 distribution of Ni and Si on sites 4d and 4e, respectively,
corresponds to a modulation vector [0, 0, 1] with respect to the space group I4/mmm of the ThMn12 structure. TbNi10Si2 orders antiferromagnetically below T
N
= 4.5 K with a magnetic propagation vector of [0, 0, 1/2]. The magnetic Tb moments, 8.97(2) /Tb atom at 1.6 K, are aligned along the c-axis. The Ni sites in TbNi10Si2 do not carry any ordered magnetic moments. The compounds with R
=
Dy, Ho, Er, and Tm are paramagnetic down to 1.6 K and 3.0 K, respectively.
Received 10 July 2002 / Received in final form 12 September 2002 Published online 29 October 2002 相似文献