全文获取类型
收费全文 | 3105篇 |
免费 | 125篇 |
国内免费 | 19篇 |
专业分类
化学 | 2303篇 |
晶体学 | 18篇 |
力学 | 113篇 |
数学 | 201篇 |
物理学 | 614篇 |
出版年
2023年 | 18篇 |
2022年 | 46篇 |
2021年 | 70篇 |
2020年 | 71篇 |
2019年 | 74篇 |
2018年 | 36篇 |
2017年 | 42篇 |
2016年 | 110篇 |
2015年 | 90篇 |
2014年 | 137篇 |
2013年 | 218篇 |
2012年 | 256篇 |
2011年 | 282篇 |
2010年 | 164篇 |
2009年 | 133篇 |
2008年 | 212篇 |
2007年 | 196篇 |
2006年 | 173篇 |
2005年 | 147篇 |
2004年 | 117篇 |
2003年 | 102篇 |
2002年 | 134篇 |
2001年 | 55篇 |
2000年 | 44篇 |
1999年 | 29篇 |
1998年 | 14篇 |
1997年 | 18篇 |
1996年 | 22篇 |
1995年 | 19篇 |
1994年 | 20篇 |
1993年 | 15篇 |
1992年 | 12篇 |
1991年 | 6篇 |
1990年 | 6篇 |
1989年 | 12篇 |
1988年 | 9篇 |
1987年 | 11篇 |
1986年 | 10篇 |
1985年 | 14篇 |
1984年 | 15篇 |
1981年 | 5篇 |
1980年 | 8篇 |
1977年 | 8篇 |
1976年 | 4篇 |
1975年 | 5篇 |
1974年 | 12篇 |
1973年 | 6篇 |
1972年 | 5篇 |
1971年 | 5篇 |
1970年 | 4篇 |
排序方式: 共有3249条查询结果,搜索用时 11 毫秒
81.
82.
A connection which is both Einstein and semisymmetric is called anES connection, and a generalizedn-dimensional Riemannian manifold on which the differential geometric structure is imposed by a unified field tensorg
through anES connection is called ann-dimensionalES manifold and denoted byESX
n
. We investigate some necessary and sufficient conditions for submanifolds ofESX
n
to be also Einstein and derive the generalized fundamental equations on various submanifolds ofESX
n
, such as generalized Gauss formulas, generalized Weingarten equations, and generalized Gauss-Codazzi equations. We employ the useful and powerful concept ofC-nonholonomic frame of reference, introduced in earlier work. 相似文献
83.
A C1-class of plane closed curves is considered, which contains all ovals and rosettes. This class is divided into some subclasses for which greatest lower bounds of numbers of antipodal and arc-antipodal sets are determined. 相似文献
84.
Nishii Y Wakasugi K Koga K Tanabe Y 《Journal of the American Chemical Society》2004,126(17):5358-5359
Chirality exchange benzannulation of optically active (1S)-aryl(aryl')-2,2-dichlorocyclopropylmethanols (>99% ee) using TiCl4 successfully proceeded to give axially chiral (M)-alpha-arylnaphthalenes with excellent levels of stereo induction (>99% ee). This unique transformation involves the single-step chirality exchange from sp3 central chirality to axial chirality, that is, a type of excellent memory effect. 相似文献
85.
Kyung‐Youl Baek Masami Kamigaito Mitsuo Sawamoto 《Journal of polymer science. Part A, Polymer chemistry》2002,40(12):1937-1944
A series of functionalized 2‐bromoisobutyrates and 2‐chloro‐2‐phenylacetates led to α‐end‐functionalized poly(methyl methacrylate)s in Ru(II)‐catalyzed living radical polymerization; the terminal functions included amine, hydroxyl, and amide. These initiators were effective in the presence of additives such as Al(Oi‐Pr)3 and n‐Bu3N. The chlorophenylacetate initiators especially coupled with the amine additive gave polymers with well‐controlled molecular weights (Mw/Mn = 1.2–1.3) and high end functionality (Fn ~ 1.0). © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1937–1944, 2002 相似文献
86.
Kim Y Choi YH Chin YW Jang YP Kim YC Kim J Kim JY Joung SN Noh MJ Yoo KP 《Journal of chromatographic science》1999,37(12):457-461
An investigation of the effect of plant matrix on the supercritical fluid extraction efficiency of five schisandrin derivatives is reported, exhibiting a great difference with respect to extraction efficiency depending on the matrix. Pure supercritical CO2 at 60 degrees C and 34.0 MPa cannot fully recover schisandrin derivatives from the leaves as much as from the other matrices. Only 36.9% of these compounds are extracted from leaves of Schisandra chinensis by supercritical CO2 in comparison with organic solvent extraction. However, more than 80% of schisandrin derivatives are obtained from both stem and fruit parts. Ethanol addition also shows a different effect depending on plant matrix; that is, CO2 modified with 10% ethanol could enhance the yield of schisandrin derivatives from leaves by four times when compared with that of pure CO2, but it has little effect on both stems and fruits. 相似文献
87.
We synthesized a novel colorimetric anion chemosensor bearing benzimidazole motifs as recognition sites in the pods of the receptor. The addition of tetrabutylammonium salts of F− or AcO− to the solution of receptor caused dramatic color changes from colorless to yellow, which was clearly visible to the naked eye. The receptor showed no significant changes on addition of other anions such as Cl−, Br−, I−, NO3−, and H2PO4−. 相似文献
88.
We have investigated atomic and electronic structures of hydrogen-chemisorbed single-walled carbon nanotubes (SWCNTs) by density functional calculations. We have searched for relative stability of various hydrogen adsorption geometries with coverage. The hydrogenated SWCNTs are stable with coverage of H/C, theta >/= 0.3. The circular cross sections of nanotubes are transformed to polygonal shapes with different symmetries upon hydrogen adsorption. We find that the band gap in carbon nanotubes can be engineered by varying hydrogen coverage, independent of the metallicity of carbon nanotubes. This is explained by the degree of sp(3) hybridization. 相似文献
89.
Chung HS Park SR Choi EK Park HJ Griffin RJ Song CW Park H 《Experimental & molecular medicine》2003,35(3):181-188
The role of sphingomyelinase (SMase) activation and mitogen activated protein kinases (MAPKs) activation in cellular apoptosis was investigated during the hyperthermic treatment of HL-60 human leukemia cells. Treating the cells for 1 h at 43(o)C caused more than 50% of cellular apoptosis within several hours. The neutral-SMase activity in the cells treated for 1 h at 42(o)C was slightly increased but decreased in the cells treated at 43(o)C or 44(o)C for the same period whereas the acid SMase activity was slightly increased after heating the cells at 42(o)C and 43(o)C and markedly increased at 44(o)C for 1 h. Treatment of cells with inhibitors of SMase activation and ceramide formation significantly reduced the heat-induced apoptosis. Three major families of mitogen-activated protein kinases (MAPKs), i.e. ERK1/2, p38 and JNK, were activated by the hyperthermic treatment of cells. Inhibition of ERK1/2 with PD98059 exerted little effect on the heat-induced apoptosis and p38 inhibition with SB203580 slightly lessened apoptosis whereas, inhibition of JNK with SP600125 markedly suppressed the heat-induced apoptosis. These results indicate that heat-shock induced the activation of SMase, particularly acid-SMase, thereby causing apoptosis and that JNK played a pivotal role in heat-induced apoptosis in HL-60 leukemia cells. 相似文献
90.
Xi Xing Beth Reed Mi Kyung Bahng Peng Wang Hin Koo Woo Sun Jong Baek Chee Shing Lam Cheuk Yiu Ng¤ 《化学物理学报(中文版)》2008,21(3):193-201
We show that by scanning the frequency of a single mode infrared (IR) optical parametric oscillator (IR-OPO) laser to excite the molecular species of interest and fixing the frequency of a vacuum ultraviolet (VUV) laser to photoionize the IR excited species, high-resolution IR spectra of polyatomic neutrals can be obtained with high sensitivity. The fact that this IR-VUV-photoion (IR-VUV-PI) method is based on VUV photoionization probe, and thus, allows the identification of the neutral IR absorber, makes it applicable for IR spectroscopy measurements of isotopemers, radicals, and clusters, which usually exist as impure samples. The highly resolved IR-VUV-PI measurements achieved using the single mode IR-OPO laser have made possible the selection of single rovibrational states of CH3X (X=Br and I), C2H4, and C3H4 for VUV-pulsed field ionization-photoelectron (VUV-PFI-PE) measurements, resulting in rovibrationally resolved photoelectron spectra for these polyatomic molecules. These experiments show that the signal-to-noise ratios of the IR-VUV-PI and IR-VUV-PFI-PE spectra obtained by employing the high-resolution IR-OPO laser are significantly higher than those observed in previous IR-VUV-PI and IR-VUV-PFI-PE studies using a low-resolution IR-OPO laser. Further improvement in sensitivity of IR-VUV-PI and IR-VUV-PFI-PE measurements by using the collinear arrangement of IR-VUV lasers and molecular beam is discussed. 相似文献