全文获取类型
收费全文 | 1277篇 |
免费 | 26篇 |
国内免费 | 7篇 |
专业分类
化学 | 1012篇 |
晶体学 | 4篇 |
力学 | 18篇 |
数学 | 108篇 |
物理学 | 168篇 |
出版年
2023年 | 9篇 |
2022年 | 11篇 |
2021年 | 9篇 |
2020年 | 15篇 |
2019年 | 9篇 |
2018年 | 14篇 |
2017年 | 9篇 |
2016年 | 24篇 |
2015年 | 19篇 |
2014年 | 27篇 |
2013年 | 65篇 |
2012年 | 73篇 |
2011年 | 101篇 |
2010年 | 45篇 |
2009年 | 66篇 |
2008年 | 64篇 |
2007年 | 75篇 |
2006年 | 88篇 |
2005年 | 65篇 |
2004年 | 66篇 |
2003年 | 54篇 |
2002年 | 62篇 |
2001年 | 16篇 |
2000年 | 21篇 |
1999年 | 16篇 |
1998年 | 16篇 |
1997年 | 18篇 |
1996年 | 14篇 |
1995年 | 9篇 |
1994年 | 16篇 |
1993年 | 11篇 |
1992年 | 13篇 |
1991年 | 11篇 |
1990年 | 17篇 |
1989年 | 9篇 |
1988年 | 6篇 |
1986年 | 8篇 |
1985年 | 21篇 |
1984年 | 13篇 |
1983年 | 13篇 |
1982年 | 13篇 |
1981年 | 9篇 |
1980年 | 9篇 |
1979年 | 15篇 |
1978年 | 4篇 |
1976年 | 4篇 |
1975年 | 4篇 |
1974年 | 7篇 |
1971年 | 6篇 |
1968年 | 4篇 |
排序方式: 共有1310条查询结果,搜索用时 15 毫秒
71.
Toshiyuki Abe Geoffrey Buhl Chongying Dong 《Transactions of the American Mathematical Society》2004,356(8):3391-3402
We demonstrate that, for vertex operator algebras of CFT type, -cofiniteness and rationality is equivalent to regularity. For -cofinite vertex operator algebras, we show that irreducible weak modules are ordinary modules and -cofinite, is -cofinite, and the fusion rules are finite.
72.
Lordi V Gambin V Friedrich S Funk T Takizawa T Uno K Harris JS 《Physical review letters》2003,90(14):145505
Ga(1-x)In(x)N(y)As(1-y) is a promising material system for the fabrication of inexpensive "last-mile" optoelectronic components. However, details of its atomic arrangement and the relationship to observed optical properties is not fully known. Particularly, a blueshift of emission wavelength is observed after annealing. In this work, we use x-ray absorption fine structure to study the chemical environment around N atoms in the material before and after annealing. We find that as-grown molecular beam epitaxy material consists of a nearly random distribution of atoms, while postannealed material shows segregation of In toward N. Ab initio simulations show that this short-range ordering creates a more thermodynamically stable alloy and is responsible for blueshifting the emission. 相似文献
73.
(--)-Muricatacin, a potent cytotoxic (4R,5R)-5-hydroxyheptadecan-4-olide, has been synthesized through alpha-C--H hydroxyalkylation and alpha'-C--H oxidation of tetrahydrofuran. This study presents a novel method for C--H bond functionalization as a means for preparing gamma-(hydroxyalkyl)-gamma-butyrolactones. 相似文献
74.
Murakami T Nishikiori T Nohira T Ito Y 《Journal of the American Chemical Society》2003,125(2):334-335
Ammonia was successfully synthesized by using a new electrochemical reaction with high current efficiency at atmospheric pressure and at lower temperatures than the Haber-Bosch process. In this method, nitride ion (N3-), which is produced by the reduction from nitrogen gas at the cathode, is anodically oxidized and reacts with hydrogen to produce ammonia at the anode. 相似文献
75.
76.
Takayanagi T 《The Journal of chemical physics》2005,122(24):244307
Ab initio electronic structure calculations have been performed for (CH(3)CN)(2) (-) and (CH(3)CN)(3) (-) cluster anions using a diffuse basis set. We found both the dipole-bound structures and internal structures, where in the former structure an excess electron is mainly distributed on the surface of the cluster while an excess electron is internally trapped in the latter configuration. The optimized structures found for cluster anions were compared to those for neutral clusters. Potential-energy surfaces were also plotted as a function of appropriate internal coordinates in order to understand the interconversions of the optimized structures of clusters. The relative stabilities of the optimized confirmers have been discussed on the basis of the characteristics of these potential surfaces, relative energies, and electron vertical detachment energies. 相似文献
77.
Hashidzume A Matsumoto A Mori T Shikata T Sato T 《Langmuir : the ACS journal of surfaces and colloids》2012,28(13):5522-5526
This letter describes the phase behavior of aqueous solutions of an N-isopropylacrylamide (NIPAM) homopolymer and copolymers of N,N'-diisopropylfumaramide (DIPFAM) and NIPAM as studied by transmittance measurements, infrared spectroscopy, and differential scanning calorimetry to reveal the effect of the density of N-isopropylamide side chain upon the phase behavior. The clouding-point and clearing-point temperatures decreased with increasing the mole fraction of DIPFAM (x(D)). It was noteworthy that only an extra side chain per ca. 7 NIPAM units had a remarkable effect on the phase behavior; the interactions between side chains were stronger, the intrapolymer contraction was less favorable, and the cooperativity of phase transition was lower at x(D) = 0.15 presumably because of the steric hindrance of dense side chains. 相似文献
78.
The characteristic fragment ions and visualization of cationic starches on pulp fiber using ToF‐SIMS
Yasuyuki Matsushita Takuya Sekiguchi Kaori Saito Toshiyuki Kato Takanori Imai Kazuhiko Fukushima 《Surface and interface analysis : SIA》2007,39(6):501-505
Time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) was used to investigate the distribution of cationic starch on pulp fiber. To identify the characteristic fragment ions of the cationic starches, deuterium‐labeled cationic starches were prepared and analyzed using ToF‐SIMS. The starch 2‐hydroxypropyltrimethylammonium chloride derivative generated characteristic fragments at m/z 58 and 59, which were identified as [H2C?N(CH3)2]+ and [N(CH3)3]+·, respectively. The fragmentation patterns were also suggested. From the imaging analysis, the adsorption of the cationic starch on fibers was uneven on individual fibers, as well as between fibers. This may have been on account of fiber morphology and structure. On examining scanning electron microscope (SEM) images, the quaternary ammonium starch derivative (QS) did not penetrate the fiber. No migration of cationic starch was observed under various drying conditions. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
79.
Toshinobu Higashimura Yoshitsugu Hirokawa Kei Matsuzaki Toshiyuki Uryu 《Journal of polymer science. Part A, Polymer chemistry》1980,18(5):1489-1498
Acetal additions to β-substituted vinyl ethers having a variety of substituents (alkenyl ethers) were stereochemically investigated as model reactions for their cationic polymerization. The reactions catalyzed by BF3O(C2H5)2 in CH2Cl2 at O°C gave 1:1 adducts, the steric structure of which was determined by means of 13C-NMR spectroscopy. trans-Alkenyl ethers always gave adducts with a single structure stereospecifically, indicating that the intermediate carbocation attacks a trans-alkenyl ether from a definite direction independent of the bulkiness of substituents. On the other hand, cis-alkenyl ethers formed adducts with two steric structures, and the direction of cation addition was found to depend on the bulkiness of the alkoxy group involved. The above trends were in agreement with the results for poly(alkenyl ether)s and allowed detailed discussion of the stereochemistry of the propagation processes in alkenyl ether polymerizations. 相似文献
80.
Photoinduced Charge‐Transfer State of 4‐Carbazolyl‐3‐(trifluoromethyl)benzoic Acid: Photophysical Property and Application to Reduction of Carbon−Halogen Bonds as a Sensitizer 下载免费PDF全文
Prof. Dr. Ryosuke Matsubara Toshiyuki Shimada Prof. Dr. Yasuhiro Kobori Tatsushi Yabuta Prof. Dr. Toshiyuki Osakai Prof. Dr. Masahiko Hayashi 《化学:亚洲杂志》2016,11(14):2006-2010
The photoinduced persistent intramolecular charge‐transfer state of 4‐carbazolyl‐3‐(trifluoromethyl)benzoic acid was confirmed. It showed a higher catalytic activity in terms of yield and selectivity in the photochemical reduction of alkyl halides compared to the parent carbazole. Even unactivated primary alkyl bromides could be reduced by this photocatalyst. The high catalytic activity is rationalized by considering the slower backward single‐electron transfer owing to the spatial separation of the donor and acceptor subunits. 相似文献