全文获取类型
收费全文 | 5711篇 |
免费 | 671篇 |
国内免费 | 562篇 |
专业分类
化学 | 4383篇 |
晶体学 | 84篇 |
力学 | 240篇 |
综合类 | 50篇 |
数学 | 728篇 |
物理学 | 1459篇 |
出版年
2024年 | 5篇 |
2023年 | 51篇 |
2022年 | 131篇 |
2021年 | 129篇 |
2020年 | 151篇 |
2019年 | 197篇 |
2018年 | 177篇 |
2017年 | 128篇 |
2016年 | 253篇 |
2015年 | 247篇 |
2014年 | 314篇 |
2013年 | 421篇 |
2012年 | 425篇 |
2011年 | 476篇 |
2010年 | 336篇 |
2009年 | 313篇 |
2008年 | 421篇 |
2007年 | 362篇 |
2006年 | 345篇 |
2005年 | 301篇 |
2004年 | 255篇 |
2003年 | 249篇 |
2002年 | 298篇 |
2001年 | 242篇 |
2000年 | 149篇 |
1999年 | 103篇 |
1998年 | 58篇 |
1997年 | 44篇 |
1996年 | 44篇 |
1995年 | 31篇 |
1994年 | 26篇 |
1993年 | 25篇 |
1992年 | 14篇 |
1991年 | 15篇 |
1990年 | 13篇 |
1989年 | 8篇 |
1988年 | 13篇 |
1987年 | 18篇 |
1986年 | 15篇 |
1985年 | 17篇 |
1984年 | 15篇 |
1983年 | 7篇 |
1982年 | 10篇 |
1981年 | 14篇 |
1980年 | 14篇 |
1979年 | 5篇 |
1978年 | 7篇 |
1976年 | 6篇 |
1975年 | 10篇 |
1974年 | 9篇 |
排序方式: 共有6944条查询结果,搜索用时 15 毫秒
41.
42.
43.
In this paper we introduce a new notion of infine nonsmooth functions and give several characterizations of infineness property. We prove alternative theorems with mixed constraints (i.e., inequality and equality constraints) being described by invex-infine nonsmooth functions. We establish a necessary and sufficient condition for a solution of a vector optimization problem involving mixed constraints to be a properly efficient solution. 相似文献
44.
Binyuan Liu Yang Li Boo‐Gyo Shin Do Yeung Yoon IL Kim Li Zhang Weidong Yan 《Journal of polymer science. Part A, Polymer chemistry》2007,45(15):3391-3399
Three novel functionalized polynorbornenes (PNB) with pendant dimethyl carboxylate group (carboxylates—acetate, propionate, and butyrate) are synthesized as a vinyl‐type with a palladium (II) catalyst in high yield. The effects of size of substitutents, molar ratio of monomer to catalyst, solvent polarity, reaction time, and temperature on the polymerization of exo‐norbornene dimethyl propionate were systematically investigated. The low molar ratio and temperature, as well as high polarity of solvent, and long reaction time, are favorable for the enhancement of the monomer conversion, especially, the solvent have an obvious effect on the catalyst activity. The resulting poly(cis‐norbornene‐exo‐2,3‐dimethyl carboxylates) (PNB‐dimethyl carboxylates) show good solubility in common organic solvent and high thermal stability up to 360 °C. The glass transition temperature was detected by DMA at 331, 324, and 318 °C for acetate, propionate, and butyrate, respectively. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3391–3399, 2007 相似文献
45.
Measurement of small-signal and large-signal responses of packaged laser modules at high temperature
Ning Hua Zhu Ji Min Wen Hai Peng Song Shang Jian Zhang Liang Xie 《Optical and Quantum Electronics》2006,38(15):1245-1257
In this paper, the pulsed injection method is extended to measure the chip temperature of various packaged laser modules,
such as the DFB laser modules, the FP laser modules, and the EML laser modules. An optimal injection condition is obtained
by investigating the dependence of the lasing wavelength on the width and period of the injection pulse in a relatively wide
temperature range. The small-signal frequency responses and large-signal performances of packaged laser modules at different
chip temperature are measured. The adiabatic small-signal modulation characteristics of packaged LD are first extracted. In
the large-signal measurement, the effects of chip temperature, bias current and driving signal on the performances of the
laser modules are discussed. It has been found that the large-signal performances of the EML modules depend on the different
red-shift speeds of the DFB and EAM sections as chip temperature varying, and the optimal characteristics may be achieved
at higher temperature. 相似文献
46.
The coapproximation in linear spaces 总被引:2,自引:0,他引:2
Son Wenhua 《分析论及其应用》1993,9(4):55-65
In this paper, we investigate the properties of strongly coapproximation in normed linear spaces and locally convex spaces.
The relations between strongly coapproximation and strongly unique approximation and of the f-coapproximation and f-approximation
are also considered.
Supported by NSFC 相似文献
47.
John R. Peterson Tamara J. Winter Hoang D. Do Robin D. Rogers 《Journal of chemical crystallography》1989,19(1):135-145
Structural and conformational information obtained from the crystal structure and solution1H nmr investigations of the title compound are compared. The 4-aryltetralone, C24H24O10, crystallizes as a chloroform solvate in the monoclinic space group, P21/n, witha=12.519(4),b=17.938(6),c=12.534(9)Å,=111.90(5)°, and Dcalc=1.51 g cm–3 forZ=4. The data for this compound were collected at –150°C. Least-squares refinement of 2796 observed [F
o5(F
o)] reflections led to the final agreement index ofR=0.062. A threefold static disorder was observed for one of the carboxyl groups. The second carboxyl group participates in an intramolecular hydrogen bond and is thus ordered. The1H nmr spectrum revealed the title compound to exist as a keto-enol tautomeric mixture in solution. Vicinal hydrogen coupling constant analysis proved reliable in ascertaining B-ring stereochemistry of 2,3-disubstituted-4-aryltetralones. 相似文献
48.
Kim GN Kim EJ Son D Bacala A Imlay R Kirk P McNeil RR Metcalf W Cheng CP Mao ZP Yan Y Xu YT Zhu YC Abashian A Gotow K Kajino F Low E Naito F Piilonen L Childers R Darden C Lusin S Rosenfeld C Wilson S Frautschi M Kagan H Kass R Trahern CG Ko W Lander RL Maeshima K Malchow RL Higashi JR Kurihara Y Maki A Nozaki T Omori T Perez P Sagawa H Sakai Y Sugimoto Y Takaiwa Y Terada S Tsuchiya K Poling R Green J Park IH Sakamoto S Sannes F Schnetzer S Stone R Trentalange S Zimmerman D Miyano K Miyata H 《Physical review letters》1988,61(8):911-914
49.
Xu Wen-Yang Guo Chang-Jie Do Tao 《Journal of inclusion phenomena and macrocyclic chemistry》1986,4(4):325-331
A member of the novel family of crystalline microporous aluminophosphates, AlPO4-12, was synthesized by hydrothermal crystallization using different aluminum-containing compounds. Three new crystalline phases were obtained by varying the composition of the reaction mixture. The effect of the synthesis conditions on the hudrothermal process and the kinetics of crystallization are discussed. The apparent activation energies obtained for AlPO4-12 are 20.9 and 14.6 kcal/mol for nucleation and crystallization, respectively. The adsorption isotherms of one AlPO4-12 product were measured. 相似文献
50.