全文获取类型
收费全文 | 9026篇 |
免费 | 311篇 |
国内免费 | 75篇 |
专业分类
化学 | 6608篇 |
晶体学 | 41篇 |
力学 | 204篇 |
数学 | 1356篇 |
物理学 | 1203篇 |
出版年
2023年 | 33篇 |
2021年 | 108篇 |
2020年 | 145篇 |
2019年 | 141篇 |
2018年 | 101篇 |
2017年 | 73篇 |
2016年 | 220篇 |
2015年 | 190篇 |
2014年 | 222篇 |
2013年 | 514篇 |
2012年 | 539篇 |
2011年 | 682篇 |
2010年 | 307篇 |
2009年 | 237篇 |
2008年 | 518篇 |
2007年 | 598篇 |
2006年 | 626篇 |
2005年 | 503篇 |
2004年 | 459篇 |
2003年 | 393篇 |
2002年 | 361篇 |
2001年 | 134篇 |
2000年 | 88篇 |
1999年 | 84篇 |
1998年 | 80篇 |
1997年 | 107篇 |
1996年 | 113篇 |
1995年 | 85篇 |
1994年 | 80篇 |
1993年 | 90篇 |
1992年 | 73篇 |
1991年 | 56篇 |
1990年 | 82篇 |
1989年 | 44篇 |
1988年 | 58篇 |
1987年 | 59篇 |
1986年 | 70篇 |
1985年 | 107篇 |
1984年 | 103篇 |
1983年 | 68篇 |
1982年 | 95篇 |
1981年 | 93篇 |
1980年 | 94篇 |
1979年 | 68篇 |
1978年 | 84篇 |
1977年 | 62篇 |
1976年 | 58篇 |
1975年 | 52篇 |
1974年 | 32篇 |
1973年 | 60篇 |
排序方式: 共有9412条查询结果,搜索用时 296 毫秒
41.
An asymptotic formula is obtained for the number of representations of an element of a finite field as a weighted sum of two prescribed powers of primitive elements. This generalises previous work on sums of primitive elements, including that relating to some conjectures of Golomb. 相似文献
42.
Stephen L. Howard Joyce E. Newberry Rosario C. Sausa Andrzej W. Miziolek 《Journal of the American Society for Mass Spectrometry》1993,4(2):152-158
A recently developed research apparatus for characterization of low-pressure premixed flames has been developed and was used to characterize the C2H4/N2O/Ar flame at 20 torr. This instrument incorporates several diagnostic techniques in one apparatus so that individual techniques can be quantitatively compared and the usable detection range (both in terms of resolution and species detection) expanded. Results discussed in this report include mass analysis by triple quadrupole mass spectrometer and temperature measurement by thermocouple. Concentration profiles in the one-dimensional flame include CO, N2, and C2H4, at nominal m/z 28 as well as CO2 and N2O at m/z 44. 相似文献
43.
44.
Summary We discuss some recent theoretical studies of the kinetics of the collapse transition in homopolymers. An isolated polymer
is modelled using computer simulation, and a time-dependent mean-field theory. The mean-field theory is analysed analytically
for early stages, and for short polymers the equations are studied numerically. The results of simulation and theory are compared
yielding, we argue, a consistent physical picture. Quantitative comparisons are not yet given, but seem relatively promising.
Paper presented at the I International Conference on Scaling Concepts and Complex Fluids, Copanello, Italy, July 4– 1994. 相似文献
45.
46.
Stephen P. Humphries 《Israel Journal of Mathematics》2004,143(1):189-222
We prove that (with two possible exceptions) the Hurwitz braid group action on the sequence of standard generators of an irreducible
Artin group has a finite orbit if and only if the Artin group is of finite type (i.e., the corresponding Coxeter group is
finite). 相似文献
47.
Three different analytical solutions are presented for a potential vortex ring using three different streamfunctions. Verification studies confirm that all three approaches are valid. It is found that the solution obtained using the Biot–Savart law is the most efficient method due to its simplicity. It is shown that all analytical results are accurate to within machine accuracy and sample calculations are included. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
48.
49.
It is generally in a firm’s interest for its supply chain partners to invest in innovations. To the extent that these innovations either reduce the partners’ variable costs or stimulate demand for the end product, they will tend to lead to higher levels of output for all of the firms in the chain. However, in response to the innovations of its partners, a firm may have an incentive to opportunistically increase its own prices. The possibility of such opportunistic behavior creates a hold-up problem that leads supply chain partners to underinvest in innovation. Clearly, this hold-up problem could be eliminated by a pre-commitment to price. However, by making an advance commitment to price, a firm sacrifices an important means of responding to demand uncertainty. In this paper we examine the trade-off that is faced when a firm’s channel partner has opportunities to invest in either cost reduction or quality improvement, i.e. demand enhancement. Should it commit to a price in order to encourage innovation, or should it remain flexible in order to respond to demand uncertainty. We discuss several simple wholesale pricing mechanisms with respect to this trade-off. 相似文献
50.
Abhimanyu O. Patil Stephen Zushma Robert T. Stibrany Steven P. Rucker Louise M. Wheeler 《Journal of polymer science. Part A, Polymer chemistry》2003,41(13):2095-2106
Novel nickel(II) bisbenzimidazole complexes were prepared via a three‐step synthetic procedure consisting of aniline/diacid condensation, ligand N‐alkylation, and metal complexation. The complexes were characterized by X‐ray crystallography and found to possess a pseudotetrahedral geometry. Upon activation with methylaluminoxane, these nickel bisbenzimidazoles did not polymerize simple olefins (e.g., ethylene, propylene, and 1‐butene) but were found to carry out the rapid and efficient polymerization of norbornene. The polynorbornene products were characterized by gel permeation chromatography/light scattering, 13C NMR, and IR, and their Mark–Houwink and dn/dc parameters were determined. The molecular weights of the polynorbornenes were very high (weight‐average molecular weight = 587,000–797,000 g/mol). 13C NMR suggested that the polymerization occurred via vinyl addition (i.e., a 2,3‐linked polymer); no ring‐opened product was observed. Thermogravimetric analysis indicated that the polynorbornenes were stable up to 400 °C under nitrogen. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2095–2106, 2003 相似文献