全文获取类型
收费全文 | 18571篇 |
免费 | 2887篇 |
国内免费 | 2772篇 |
专业分类
化学 | 14779篇 |
晶体学 | 253篇 |
力学 | 912篇 |
综合类 | 218篇 |
数学 | 2365篇 |
物理学 | 5703篇 |
出版年
2024年 | 15篇 |
2023年 | 241篇 |
2022年 | 400篇 |
2021年 | 498篇 |
2020年 | 588篇 |
2019年 | 686篇 |
2018年 | 532篇 |
2017年 | 583篇 |
2016年 | 854篇 |
2015年 | 900篇 |
2014年 | 1133篇 |
2013年 | 1443篇 |
2012年 | 1741篇 |
2011年 | 1746篇 |
2010年 | 1271篇 |
2009年 | 1212篇 |
2008年 | 1381篇 |
2007年 | 1183篇 |
2006年 | 1045篇 |
2005年 | 951篇 |
2004年 | 857篇 |
2003年 | 699篇 |
2002年 | 760篇 |
2001年 | 621篇 |
2000年 | 439篇 |
1999年 | 389篇 |
1998年 | 293篇 |
1997年 | 231篇 |
1996年 | 227篇 |
1995年 | 171篇 |
1994年 | 181篇 |
1993年 | 141篇 |
1992年 | 126篇 |
1991年 | 122篇 |
1990年 | 95篇 |
1989年 | 80篇 |
1988年 | 66篇 |
1987年 | 46篇 |
1986年 | 51篇 |
1985年 | 45篇 |
1984年 | 17篇 |
1983年 | 13篇 |
1982年 | 12篇 |
1981年 | 11篇 |
1980年 | 9篇 |
1959年 | 13篇 |
1958年 | 11篇 |
1957年 | 15篇 |
1956年 | 10篇 |
1936年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 171 毫秒
51.
52.
研究了不同衬底-阴极距离、直流电压和H2流量对a-CH薄膜沉积速率的影响。结果表明:衬底-阴极距离必须大于0.5cm,随着该距离的增加,薄膜的沉积速率减少;直流电压达550V时沉积速率最大;随着H2含量的增加,CH4含量相对减少,沉积速率随之降低。用AFM观察了以该方法制得的448.4nm CH薄膜的表面形貌,表面粗糙度约为10nm。最后测出了不同条件下CH薄膜的UV-VIS谱,由此可以计算得到薄膜的禁带宽度及折射率。 相似文献
53.
从激光推进的要求出发,阐述了用于激光推进的高功率激光器的选择原则,即激光器必须满足:(1)高的平均功率和峰值功率;(2)高的单脉冲能量;(3)高的重复频率;(4)优良的大气传输特性。主要分析了目前YAG固体激光器、自由电子激光器和TEA脉冲CO2激光器的特点,通过上述4个方面性能的比较,认为在目前水平下,TEA脉冲CO2激光器是进行激光推进的首选强激光源,其优点表现在:功率可达10kW量级,单脉冲能量可达0.5~1kJ,重复频率为20~40Hz;激光波长处于大气传输窗口,对大气变化不敏感;工作物质快速流动,不存在热透镜效应和破坏阈值;相关光学元件易于制造;光束质量较好;运行成本低。 相似文献
54.
ZHANG Zhi-bin LI Min SONG Hong FANG Yi Hua Hui CHEN Li-guo ZHOU Wei WANG Zheng-rong 《合成化学》2004,12(Z1)
Microcapsulation is a technology that enwrapped the solid or liquid or some gas matter with membrane materials to form microparticles(i.e.microcapsules). The materials of microcapsule is composed of naturnal polymers or modified naturnal polymers or synthesized polymers. The water-soluble core matter can only use oil-soluble wall materials, and vice versa.Synthesized methods of polymer microcapsulesSynthesized methods with monomers as raw materialsThis kind of methods include suspension polymerization, emulsion polymerization, dispersal polymerization, precipitation polymerization,suspension condensation polymerization, dispersal condensation polymerization, deposition condensation polymerization, interface condensation polymerization, and so on.Synthesized methods with polymers as raw materialsThese methods are suspension cross-linked polymerization, coacervation phase separation,extraction with solvent evaporation, polymer deposition, polymer chelation, polymer gel,solidification of melting polymer, tray-painted ways, fluidized bed ways, and so forth.Polymer materials to synthesize microcapsules2.1. Naturnal polymer materialsThe characteristics of this kind of materials are easy to form membrane, good stability and no toxicity. The polymer materials include lipids(liposome), amyloses, proteins, plant gels, waxes, etc.2.2. Modified polymer materialsThe characteristics of these materials are little toxicity, high viscidity(viscosity), soluble salt materials. But they cannot be used in water, acidic environment and high temperature environment for a long time. The materials include all kind of derivants of celluloses.2.3. Synthesized polymer materialsThe characteristics of the materials are easy to form membrane, good stability and adjustment of membrane properties. The synthesized polymer materials include degradable polymers(PLA, PGA,PLGA, PCL, PHB, PHV, PHA, PEG, PPG and the like) and indegradable polymers(PA, PMMA,PAM, PS, PVC, PB, PE, PU, PUA, PVA and otherwise).The applications of polymer microcapsules in cell technologyThe "artificial cell" is the biological active microcapsule used in biological and medical fields.The applications of cells (including transgenic cells, the same as artificial cells) technology include several aspects as follows:3.1. Microcapsulation of artificial red cell3.2. Microcapsule of artificial cell of biological enzyme3.3. Microcapsule of artificial cell of magnetic material3.4. Microcapsule of artificial cell of active carbon3.5. Microcapsule of active biological cell 相似文献
55.
PinHuaLI LeiWANG MinWANG JinCanYAN 《中国化学快报》2004,15(11):1295-1298
A Glaser coupling reaction of terminal alkynes in the presence of nickel chloride withoutany organics and bases in hot water has been developed, which produces the correspondinghomo-coupling products in good yields. 相似文献
56.
Impact of the internucleotide linkage modification by inserting a methylene group to the P-O bond (—O—PO
2
—
—O— chain changed for —O—PO
2
—
—CH2—O—), on the modified oligonucleotide binding ability to the natural DNA strand was studied by molecular dynamics simulation. Complex of (dT)11 with a deoxyadenosine undecamer containing alternating modified and natural internucleotide linkage was studied as a model system. The Amber force field was completed by a set of new parameters needed to model the modified part of the nucleotide. The simulations confirmed existence of a double-helical complex the melting point of which is considerably higher than 300 K. While the thymidine (unmodified) strand possesses a B-type secondary structure, the conformation of the adenosine (modified) strand is not stable at 300 K. The -ggt conformation of the modified linkages is highly preferred, temporary jumps to the -g-gt and ggt conformations were, however, observed. 相似文献
57.
We prove that RANDOM EDGE, the simplex algorithm that always chooses a random improving edge to proceed on, can take a mildly exponential number of steps in the model of abstract objective functions (introduced by Williamson Hoke [Completely unimodal numberings of a simple polytope, Discrete Appl. Math. 20 (1988) 69-81.] and by Kalai [A simple way to tell a simple polytope from its graph, J. Combin. Theory Ser. A 49(2) (1988) 381-383.] under different names). We define an abstract objective function on the n-dimensional cube for which the algorithm, started at a random vertex, needs at least exp(const·n1/3) steps with high probability. The best previous lower bound was quadratic. So in order for RANDOM EDGE to succeed in polynomial time, geometry must help. 相似文献
58.
59.
For vertical-cavity surface-emitting lasers (VCSELs) with polarization-rotated feedback, there exist several synchronization
types such as synchronizations between total powers and synchronizations between separate polarization modes. Based on the
two-mode rate equations, we study and compare numerically the performances of different synchronization types. Our results
show that three synchronization types exhibit good performances when their synchronization conditions are satisfied. They
are the complete synchronization between total powers, complete synchronization between x-polarized modes, and generalized synchronization between x-polarized and y-polarized modes. The former two types are sensitive to the injection rate and spontaneous emission, while the third type
is contrary. Synchronization type with the best performance may switch from one to another, with changing of injection rate
and spontaneous emission factor. 相似文献
60.