全文获取类型
收费全文 | 178807篇 |
免费 | 17772篇 |
国内免费 | 10427篇 |
专业分类
化学 | 93058篇 |
晶体学 | 1929篇 |
力学 | 13041篇 |
综合类 | 534篇 |
数学 | 42773篇 |
物理学 | 55671篇 |
出版年
2024年 | 370篇 |
2023年 | 2136篇 |
2022年 | 3647篇 |
2021年 | 4058篇 |
2020年 | 4250篇 |
2019年 | 4138篇 |
2018年 | 13045篇 |
2017年 | 12645篇 |
2016年 | 10746篇 |
2015年 | 5717篇 |
2014年 | 6293篇 |
2013年 | 8073篇 |
2012年 | 12939篇 |
2011年 | 19598篇 |
2010年 | 11679篇 |
2009年 | 11788篇 |
2008年 | 12763篇 |
2007年 | 14290篇 |
2006年 | 5667篇 |
2005年 | 5844篇 |
2004年 | 4844篇 |
2003年 | 4530篇 |
2002年 | 3371篇 |
2001年 | 2212篇 |
2000年 | 2048篇 |
1999年 | 2224篇 |
1998年 | 2035篇 |
1997年 | 1861篇 |
1996年 | 2084篇 |
1995年 | 1616篇 |
1994年 | 1534篇 |
1993年 | 1258篇 |
1992年 | 1123篇 |
1991年 | 1045篇 |
1990年 | 841篇 |
1989年 | 621篇 |
1988年 | 524篇 |
1987年 | 439篇 |
1986年 | 431篇 |
1985年 | 364篇 |
1984年 | 283篇 |
1983年 | 190篇 |
1982年 | 183篇 |
1981年 | 144篇 |
1980年 | 122篇 |
1979年 | 88篇 |
1978年 | 68篇 |
1976年 | 52篇 |
1974年 | 56篇 |
1973年 | 56篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
Christiane Albrecht 《Analytical and bioanalytical chemistry》2008,390(5):1223-1224
62.
63.
A two-step swelling procedure was adopted to synthesize mono-dispersed and highly cross-linked poly (St-divinylbenzene) particles
with PSt micro-spheres (1.80 μm in diameter). The PSt micro-spheres were prepared by a dispersion polymerization method and
used as seeds. The effects of monomer concentration, ratio of ethanol to water, swelling reagents, crosslinking reagents,
swelling temperature and agitation speed on particle size were investigated in detail. The morphologies and size distributions
of these micro-spheres were examined by SEM and particle size analysis (PSA). The T
g of the micro-spheres was measured by DSC. The results indicate that the particles (6.20 μm in diameter) exhibit excellent
mono dispersed property and high crosslinking degree when the concentration of the swelling reagent was 25%, the concentration
of the crosslinking reagents was 23%, the swelling temperature was 30°C and the stirring speed was 150 r/min.
__________
Translated from Chinese Journal of Applied Chemistry, 2007, 24(11): 1289–1294 相似文献
64.
Chengzhi Qi Mingyang Wang Qihu Qian Jianjie Chen 《Moscow University Mechanics Bulletin》2008,63(5):113-121
The formation mechanisms for the structural hierarchy in geological media are discussed. It is shown that the formation of such a hierarchy is caused by certain external and internal circumstances. The first ones consist in the fact that, because of external actions, the Earth’s poles continuously execute the translational and rotational motions responsible for a regular structure of rock fracture and for the appearance of the scale factor √2. The second ones consist in the fact that, under the action of many random factors and because of external actions, during the formation of geological media there appear dissipative structures and, hence, some self-similar fractal structures are formed. 相似文献
65.
M C Testik J K Cochran G C Runger 《The Journal of the Operational Research Society》2004,55(3):233-239
We study the short-term staffing problem of systems that experience random, non-stationary demand. The typical method to accommodate changes in arrival rate is to use historical data to identify peak periods and associated forecasting for upcoming time windows. In this paper, we develop a method that instead detects change as it happens. Motivated by an automatic call distributor system in a call centre with time-varying arrivals, we propose a change detection algorithm based upon non-homogeneous Poisson processes. The proposed method is general and may be thought of as a feed-forward strategy, in which we detect a change in the arrival process, estimate the new magnitude of the arrival rate, and assign an appropriate number of servers to the tasks. The generalized likelihood ratio statistic is used and a recommendation for its decision limit is developed. Simulation results are used to evaluate the performance of the detector in the context of a telephone call centre. 相似文献
66.
This paper considers a receiver set partitioning and sequencing problem in a wavelength division multiplexing single-hop lightwave network for multicasting traffic. The problem is analysed in the approach of uncapacitated single batch-processing machine scheduling. In the analysis, several solution properties are characterized with respect to a mean flow time measure, based upon which two heuristic algorithms are developed, along with a dynamic programming algorithm. Several numerical experiments show that the heuristic algorithms generate good schedules. The problem is extended to consider two measures simultaneously including the mean flow time and the number of transmissions, for which the proposed algorithms also perform well. 相似文献
67.
Guobao Zhang Jianming Zhang Shenguo Wang Deyan Shen 《Journal of Polymer Science.Polymer Physics》2003,41(1):23-30
Blends of amorphous poly(DL‐lactide) (DL‐PLA) and crystalline poly(L‐lactide) (PLLA) with poly(methyl methacrylate) (PMMA) were prepared by both solution/precipitation and solution‐casting film methods. The miscibility, crystallization behavior, and component interaction of these blends were examined by differential scanning calorimetry. Only one glass‐transition temperature (Tg) was found in the DL‐PLA/PMMA solution/precipitation blends, indicating miscibility in this system. Two isolated Tg's appeared in the DL‐PLA/PMMA solution‐casting film blends, suggesting two segregated phases in the blend system, but evidence showed that two components were partially miscible. In the PLLA/PMMA blend, the crystallization of PLLA was greatly restricted by amorphous PMMA. Once the thermal history of the blend was destroyed, PLLA and PMMA were miscible. The Tg composition relationship for both DL‐PLA/PMMA and PLLA/PMMA miscible systems obeyed the Gordon–Taylor equation. Experiment results indicated that there is no more favorable trend of DL‐PLA to form miscible blends with PMMA than PLLA when PLLA is in the amorphous state. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 23–30, 2003 相似文献
68.
J.J. Pan Xiangdong Qiu Kejian Guan Liang Dong FengQing Zhou Wei Wang Mingjie Zhang James Guo Jun Yang Chunmeng Wu 《光学学报》2003,23(Z1)
A low cost, coolerless 980nm diode pumped, gain flattened L band EDFA with fast transient control, high pump efficiency and gain clamping effect was realized by using FBGs as C band seed generators. 相似文献
69.
C Guéret N Jussien O Lhomme C Pavageau C Prins 《The Journal of the Operational Research Society》2003,54(5):458-465
In this paper, we describe an aircraft loading problem submitted by the French military agency (DGA) as part of a more general military airlift planning problem. It can be viewed as a kind of bi-dimensional bin-packing problem, with heterogeneous bins and several additional constraints. We introduce two-phase methods for solving this NP-hard problem. The first phase consists in building good initial solutions, thanks to two fast algorithms: a list-based heuristic and a loading pattern generation method. Both algorithms call a constraint-based subroutine, able to determine quickly if the items already loaded can be reshuffled to accommodate a new object. The second phase improves these preliminary solutions using local search techniques. Results obtained on real data sets are presented. 相似文献
70.