全文获取类型
收费全文 | 28319篇 |
免费 | 1053篇 |
国内免费 | 174篇 |
专业分类
化学 | 19135篇 |
晶体学 | 263篇 |
力学 | 949篇 |
综合类 | 1篇 |
数学 | 2525篇 |
物理学 | 6673篇 |
出版年
2023年 | 154篇 |
2022年 | 426篇 |
2021年 | 504篇 |
2020年 | 450篇 |
2019年 | 471篇 |
2018年 | 355篇 |
2017年 | 326篇 |
2016年 | 762篇 |
2015年 | 679篇 |
2014年 | 863篇 |
2013年 | 1593篇 |
2012年 | 2028篇 |
2011年 | 2266篇 |
2010年 | 1368篇 |
2009年 | 1208篇 |
2008年 | 1830篇 |
2007年 | 1725篇 |
2006年 | 1619篇 |
2005年 | 1496篇 |
2004年 | 1327篇 |
2003年 | 1032篇 |
2002年 | 1025篇 |
2001年 | 689篇 |
2000年 | 592篇 |
1999年 | 350篇 |
1998年 | 263篇 |
1997年 | 302篇 |
1996年 | 343篇 |
1995年 | 267篇 |
1994年 | 277篇 |
1993年 | 278篇 |
1992年 | 266篇 |
1991年 | 205篇 |
1990年 | 155篇 |
1989年 | 141篇 |
1988年 | 140篇 |
1987年 | 121篇 |
1986年 | 95篇 |
1985年 | 172篇 |
1984年 | 115篇 |
1983年 | 102篇 |
1982年 | 126篇 |
1981年 | 92篇 |
1980年 | 80篇 |
1978年 | 83篇 |
1977年 | 85篇 |
1976年 | 95篇 |
1975年 | 103篇 |
1974年 | 81篇 |
1973年 | 105篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
91.
92.
Thermotropic copolyester fibers of oxynaphthoate and oxybenzoate have been subjected to conditions that promote solid-state polymerization as well as annealing. The annealing process causes the crystals to perfect with a simultaneous increase in heat of fusion and melting temperature. Solid-state polymerization, a reaction rate-controlled process, causes the polymer viscosity average molecular weight to increase by chain extension from about 14,000 g/mole to more than 87,000 g/mole with a simultaneous impressive increase in tenacity from about 10 g/d (1.2 GPa) to almost 30 g/d (3.7 GPa). To understand the changes in mechanical properties, we have modeled the fiber structure as short rod-like molecules poorly bonded to a continuous matrix of parallel molecules. Lengthening of the reinforcing molecules facilitates better transfer of load from matrix to molecules, resulting in higher tenacity fibers. © 1994 John Wiley & Sons, Inc. 相似文献
93.
Chi Kin Chau Kwang Mong Sim 《Operations Research Letters》2003,31(5):327-334
By showing that there is an upper bound for the price of anarchyρ(Γ) for a non-atomic congestion game Γ with only separable cost maps and fixed demands, Roughgarden and Tardos show that the cost of forgoing centralized control is mild. This letter shows that there is an upper bound for ρ(Γ) in Γ for fixed demands with symmetric cost maps. It also shows that there is a weaker bound for ρ(Γ) in Γ with elastic demands. 相似文献
94.
Kuan‐Wei Lee Hong‐Cheu Lin 《Journal of polymer science. Part A, Polymer chemistry》2007,45(20):4564-4572
A series of new liquid crystalline homopolymers, copolymers, and block copolymers were polymerized from styrene‐macroinitiator ( SMi ) and methacrylates with pendent 4,4′‐bis(biphenyl)fluorene ( M1 ) and biphenyl‐4‐ylfluorene ( M2 ) groups through atom transfer radical polymerization (ATRP). The number‐average molecular weights (Mn) of polymers P1 ‐ P4 were 10,007, 14,852, 6,275, and 10,463 g mol?1 with polydispersity indices values of 1.21, 1.15, 1.31, and 1.22, respectively. All polymers exhibit the nematic phase. The thermal, mesogenic, and photoluminescent properties of all polymers were investigated. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4564–4572, 2007 相似文献
95.
Zhi‐Yong Huang Jin‐Can Shen Zhi‐Xia Zhuang Xiao‐Ru Wang Frank S. C. Lee 《应用有机金属化学》2004,18(6):255-261
Cinnabar, as one of the most widely used mineral drugs in traditional Chinese medicines, has been proven to have prominent curative effects in clinical use for more than 2000 years. But the safety and toxicity of the drug has been under constant debate in clinic usage. Metallothionein (MT) contains about 30% of cysteine in the molecule, and plays an important detoxification role against heavy metals. In this study, it was used as a biomarker to assess mercurial accumulation in rats fed orally with cinnabar. After feeding rats with cinnabar by gastric gavage at different dosages and at different times, the distribution of heavy metals (including mercury, copper and zinc) and MT was investigated among rat tissues, including liver, kidney, heart, brain, testis and blood. Metals and MT determinations were carried out using inductively coupled plasma mass spectrometry (ICP‐MS) and a modified mercury saturation assay technique respectively. The results indicated that mercury was easily accumulated in the tissues of rats exposed to cinnabar, especially in kidney. For example: at a feeding dosage of 5 g kg?1 (bw) for 4 weeks, the mercury concentrations in kidney were 13, 8.7, 21.6 and 26 times those in liver, testis, brain and heart respectively; and at 2.5 g kg?1 (bw) for 2 weeks, the mercury concentrations in kidney were 21, 2.1, 3 and 21 times those in liver, testis, brain and heart respectively. In addition, mercury in kidney and liver of all cinnabar groups was significantly higher than that of the control group (P < 0.01). A high positive correlation observed between MT concentrations and mercury levels in both liver and kidney (R2 = 0.9299, P < 0.02 for liver; R2 = 0.9923, P < 0.0008 for kidney) indicated that MT could be used as a biomarker for mercury in tissues. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
96.
An algorithm for a time accurate incompressible Navier–Stokes solver on an unstructured grid is presented. The algorithm uses a second order, three‐point, backward difference formula for the physical time marching. For each time step, a divergence free flow field is obtained based on an artificial compressibility method. An implicit method with a local time step is used to accelerate the convergence for the pseudotime iteration. To validate the code, an unsteady laminar flow over a circular cylinder at a Reynolds number of 200 is calculated. The results are compared with available experimental and numerical data and good agreements are achieved. Using the developed unsteady code, an interaction of a Karman vortex street with an elliptical leading edge is simulated. The incident Karman vortex street is generated by a circular cylinder located upstream. A clustering to the path of the vortices is achieved easily due to flexibility of an unstructured grid. Details of the interaction mechanism are analysed by investigating evolutions of vortices. Characteristics of the interactions are compared for large‐ and small‐scale vortex streets. Different patterns of the interaction are observed for those two vortex streets and the observation is in agreement with experiment. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
97.
This paper presents an operator‐splitting method (OSM) for the solution of the universal Reynolds equation. Jakobsson–Floberg–Olsson (JFO) pressure conditions are used to study cavitation in liquid‐lubricated journal bearings. The shear flow component of the oil film is first solved by a modified upwind finite difference method. The solution of the pressure gradient flow component is computed by the Galerkin finite element method. Present OSM solutions for slider bearings are in good agreement with available analytical and experimental results. OSM is then applied to herringbone grooved journal bearings. The film pressure, cavitation areas, load capacity and attitude angle are obtained with JFO pressure conditions. The calculated load capacities are in agreement with available experimental data. However, a detailed comparison of the present results with those predicted using Reynolds pressure conditions shows some differences. The numerical results showed that the load capacity and the critical mass of the journal (linear stability indicator) are higher and the attitude angle is lower than those predicted by Reynolds pressure conditions for cases of high eccentricities. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
98.
G. M. Ter-Akopian A. V. Daniel A. S. Fomichev G. S. Popeko A. M. Rodin Yu. Ts. Oganessian J. H. Hamilton A. V. Ramayya J. Kormicki J. K. Hwang D. Fong P. Gore J. D. Cole M. Jandel J. Kliman L. Krupa J. O. Rasmussen I. Y. Lee A. O. Macchiavelli P. Fallon M. A. Stoyer R. Donangelo S. -C. Wu W. Greiner 《Physics of Atomic Nuclei》2004,67(10):1860-1865
Ternary fission of 252Cf was studied at Gammasphere using eight ΔE×E particle telescopes. Helium, beryllium, boron, and carbon light charged particles (LCPs) emitted with kinetic energy more than 9, 21, 26, and 32 MeV, respectively, were identified. The 3368-keV γ transition from the first 2+ excited state in 10Be was found and the population probability ratio N(2+)/N(0+) = 0.160 ± 0.025 was estimated. No evidence was found for 3368-keV γ rays emitted from a triple molecular state. For the first time, charge distributions are obtained for ternary fission fragments emitted with helium, beryllium, and carbon LCPs. 相似文献
99.
Ha Yong Lee Se Hun Jung Soo Yong Lee Young Ho You Kyung Hyun Ko 《Applied Surface Science》2005,252(5):1891-1898
Al-Al2O3 composite coatings with different Al2O3 particle shapes were prepared on Si and Al substrate by cold spray. The powder compositions of metal (Al) and ceramic (Al2O3) having different sizes and agglomerations were varied into ratios of 10:1 wt% and 1:1 wt%. Al2O3 particles were successfully incorporated into the soft metal matrix of Al. It was found that crater formation between the coatings and substrate, which is typical characteristic signature of cold spray could be affected by initial starting Al2O3 particles. In addition, when the large hard particles of fused Al2O3 were employed, the deep and big craters were generated at the interface between coatings and hard substrates. In the case of pure soft metal coating such as Al on hard substrate, it is very hard to get proper adhesion due to lack of crater formation. Therefore, the composite coating would have certain advantages. 相似文献
100.
Logic-Based Modeling and Solution of Nonlinear Discrete/Continuous Optimization Problems 总被引:2,自引:0,他引:2
This paper presents a review of advances in the mathematical programming approach to discrete/continuous optimization problems.
We first present a brief review of MILP and MINLP for the case when these problems are modeled with algebraic equations and
inequalities. Since algebraic representations have some limitations such as difficulty of formulation and numerical singularities
for the nonlinear case, we consider logic-based modeling as an alternative approach, particularly Generalized Disjunctive
Programming (GDP), which the authors have extensively investigated over the last few years. Solution strategies for GDP models
are reviewed, including the continuous relaxation of the disjunctive constraints. Also, we briefly review a hybrid model that
integrates disjunctive programming and mixed-integer programming. Finally, the global optimization of nonconvex GDP problems
is discussed through a two-level branch and bound procedure. 相似文献