全文获取类型
收费全文 | 7064篇 |
免费 | 193篇 |
国内免费 | 48篇 |
专业分类
化学 | 4875篇 |
晶体学 | 68篇 |
力学 | 149篇 |
数学 | 664篇 |
物理学 | 1026篇 |
无线电 | 523篇 |
出版年
2023年 | 30篇 |
2022年 | 43篇 |
2021年 | 60篇 |
2020年 | 86篇 |
2019年 | 105篇 |
2018年 | 78篇 |
2017年 | 51篇 |
2016年 | 143篇 |
2015年 | 121篇 |
2014年 | 143篇 |
2013年 | 317篇 |
2012年 | 411篇 |
2011年 | 501篇 |
2010年 | 254篇 |
2009年 | 228篇 |
2008年 | 440篇 |
2007年 | 491篇 |
2006年 | 482篇 |
2005年 | 488篇 |
2004年 | 442篇 |
2003年 | 341篇 |
2002年 | 302篇 |
2001年 | 106篇 |
2000年 | 86篇 |
1999年 | 89篇 |
1998年 | 89篇 |
1997年 | 62篇 |
1996年 | 106篇 |
1995年 | 71篇 |
1994年 | 69篇 |
1993年 | 55篇 |
1992年 | 51篇 |
1991年 | 57篇 |
1990年 | 49篇 |
1989年 | 44篇 |
1988年 | 45篇 |
1987年 | 46篇 |
1986年 | 40篇 |
1985年 | 59篇 |
1984年 | 66篇 |
1983年 | 58篇 |
1982年 | 55篇 |
1981年 | 59篇 |
1980年 | 53篇 |
1979年 | 50篇 |
1978年 | 59篇 |
1977年 | 42篇 |
1976年 | 41篇 |
1975年 | 27篇 |
1974年 | 29篇 |
排序方式: 共有7305条查询结果,搜索用时 15 毫秒
31.
Brian Dipert 《电子设计技术》2003,10(8):52-62
DRAM供应商希望有朝一日一种产品大小规格能适应所有的应用要求,但各种各样的设备要求则与之相差甚远.DRAM用户也许更喜欢定制的芯片,但价格会格外昂贵.双方会在保持原则的同时作出足够的让步以达成顺利的交易么? 相似文献
32.
Faced with multiple electronic devices, service providers, and ISPs, tomorrow's mobile users might find it challenging to identify available services and acquire the rights to use them. The authors tackle this problem, combining the acquisition of role-based credentials with servicediscovery. 相似文献
33.
Manju Rajeswaran Thomas N. Blanton David R. Whitcomb Nicholas Zumbulyadis Brian J. Antalek Scott T. Misture 《Journal of solid state chemistry》2006,179(4):1053-1059
In continuation of our interest in solid-state structures of silver complexes of photographic importance, the structure for silver benzotriazole (AgBZT), has now been obtained. The preferred method for solving crystal structures is via single-crystal X-ray diffraction (XRD). However, for some materials, growing single crystals of appropriate size and quality is often difficult or even impossible. AgBZT is an example of such a silver complex with poor solubility. The usual routes to preparing single crystals using recrystallization from a cooperating solvent resulted in polycrystalline powder samples. We propose a crystal structure for AgBZT, solved from synchrotron X-ray powder diffraction data, using a direct-space Monte Carlo simulated annealing approach. AgBZT crystals are monoclinic, (P21/c), with unit cell dimensions, a=14.8052(3) Å, b=3.7498(4) Å, c=12.3495(12) Å, and β=114.200(6)°. The AgBZT complex is constructed from all three of the Benzotriazole (BZT) nitrogens bonding to a separate silver atom. As a consequence of this bonding mode, the structure is a highly cross-linked, coordination polymer. 相似文献
34.
Brian H. Davison Nhuan P. Nghiem Gerald L. Richardson 《Applied biochemistry and biotechnology》2004,114(1-3):653-669
More than 25 sorbents were tested for uptake of succinic acid from aqueous solutions. The best resins were then tested for
successive loading and regeneration using hotwater. The key desired properties for an ideal sorbent are high capacity, complete
stable regenerability, and specificity for the product. The best resins have a stable capacity of about 0.06 g of succinic
acid/g of resin at moderate concentrations (1–5 g/L) of succinic acid. Several sorbents were tested more exhaustively for
uptake of succinic acid and for successive loading and regeneration using hot water. One resin, XUS 40285, has a good stable
isotherm capacity, prefers succinate over glucose, and has good capacities at both acidic and neutral pH. Succinic acid was
removed from simulated media containing salts, succinic acid, acetic acid, and sugar using a packed column of sorbent resin,
XUS 40285. The fermentation byproduct, acetate, was completely separated from succinate. A simple hot water regeneration successfully
concentrated succinate from 10 g/L (inlet) to 40–110 g/L in the effluent. If successful, this would lower separation costs
by reducing the need for chemicals for the initial purification step. Despie promising initial results of good capacity (0.06
g of succinic/g of sorbent), 70% recovery using hot water, and a recovered concentration of >100 g/L, this regeneration was
not stable over 10 cycles in the column. Alternative regeneration schemes using acid and base were examined. Two (XUS 40285
and XFS-40422) showed both good stable capacities for succinic acid over 10 cycles and >95% recovery in a batch operation
using a modified extraction procedure combining acid and hot water washes. These resins showed comparable results with actual
broth. 相似文献
35.
Brian Dipert 《电子设计技术》2006,13(6):56-58,60,62,64,66-67
蓝色激光(Blu-ray,简称蓝光,以下同)光盘和HD DVD均开始进入量产,但格式大战的赢家还不明朗。红色激光:简称红光,以下同)格式仍是某些应用的可靠替代方案,但用户版权限制和显示器与视觉的限制使格式的未来令人疑惑。 相似文献
36.
Fabian Buffa Gustavo A. Abraham Brian P. Grady Daniel Resasco 《Journal of Polymer Science.Polymer Physics》2007,45(4):490-501
A commercially available aliphatic thermoplastic polyurethane formulated with a methylene bis(cyclohexyl) diisocyanate hard segment and a poly(tetramethylene oxide) soft segment and chain‐extended with 1,4‐butanediol was dissolved in dimethylformamide and mixed with dispersed single‐walled carbon nanotubes. The properties of composites made with unfunctionalized nanotubes were compared with the properties of composites made with nanotubes functionalized to contain hydroxyl groups. Functionalization almost eliminated the conductivity of the tubes according to the conductivity of the composites above the percolation threshold. In most cases, functionalized and unfunctionalized tubes yielded composites with statistically identical mechanical properties. However, composites made with functionalized tubes did have a slightly higher modulus in the rubbery plateau region at higher nanotube fractions. Small‐angle X‐ray scattering patterns indicated that the dispersion reached a plateau in the unfunctionalized composites that was consistent with the plateau in the rubbery plateau region. The room‐temperature modulus and tensile strength increase was proportionally higher than almost all increases seen previously in thermoplastic polyurethanes; however, the increase was still an order of magnitude below what has been reported for the best nanotube–polymer systems. Nanotube addition increased the hard‐segment glass transition temperature slightly, whereas the soft‐segment glass transition was so diffuse that no conclusions could be drawn. Unfunctionalized tubes suppressed the crystallization of the hard segment; whereas functionalized tubes had no effect. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 490–501, 2007 相似文献
37.
38.
39.
Brian Ingalls Eduardo D. Sontag Yuan Wang 《Proceedings of the American Mathematical Society》2003,131(2):487-499
The fundamental relaxation result for Lipschitz differential inclusions is the Filippov-Wazewski Relaxation Theorem, which provides approximations of trajectories of a relaxed inclusion on finite intervals. A complementary result is presented, which provides approximations on infinite intervals, but does not guarantee that the approximation and the reference trajectory satisfy the same initial condition.
40.
Veena Misra Xiaoli Xu Brian E. Hornung Richard T. Kuehn Donald S. Miles John R. Hauser Jimmie J. Wortman 《Journal of Electronic Materials》1996,25(3):527-535
In the present study, we have performed electrical characterization of oxides deposited via rapid thermal chemical vapor deposition using SiH4 and N2O. We have investigated the effect of temperature, pressure, and SiH4 to N2O ratio on the electrical and material properties of as-deposited films. We have found that as-deposited oxides deposited at low temperatures, low pressures, and with a low silane to nitrous oxide ratio of ~0.5% give good material and electrical properties. The as-deposited films are stoichiometric in nature and have high deposition rates. As-deposited films had very low Dit values, high breakdown fields, and excellent subthreshold swing. The leakage currents and metal oxide semiconductor field effect transistor current drive, although lower than thermal oxides, were found to be quite acceptable. We have also investigated the thickness dependence of the films and found that as the film thickness is reduced below 50Å, the reliability improves for all oxides including the silicon-rich deposited oxides. 相似文献