全文获取类型
收费全文 | 1323篇 |
免费 | 69篇 |
国内免费 | 4篇 |
专业分类
化学 | 743篇 |
晶体学 | 25篇 |
力学 | 48篇 |
数学 | 210篇 |
物理学 | 227篇 |
无线电 | 143篇 |
出版年
2024年 | 2篇 |
2023年 | 7篇 |
2022年 | 26篇 |
2021年 | 46篇 |
2020年 | 45篇 |
2019年 | 38篇 |
2018年 | 37篇 |
2017年 | 51篇 |
2016年 | 58篇 |
2015年 | 64篇 |
2014年 | 54篇 |
2013年 | 128篇 |
2012年 | 107篇 |
2011年 | 113篇 |
2010年 | 89篇 |
2009年 | 67篇 |
2008年 | 84篇 |
2007年 | 69篇 |
2006年 | 44篇 |
2005年 | 48篇 |
2004年 | 51篇 |
2003年 | 26篇 |
2002年 | 29篇 |
2001年 | 9篇 |
2000年 | 14篇 |
1999年 | 8篇 |
1998年 | 7篇 |
1997年 | 4篇 |
1996年 | 8篇 |
1995年 | 6篇 |
1994年 | 7篇 |
1993年 | 3篇 |
1992年 | 5篇 |
1991年 | 9篇 |
1990年 | 8篇 |
1989年 | 2篇 |
1986年 | 1篇 |
1985年 | 3篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1982年 | 3篇 |
1980年 | 2篇 |
1979年 | 3篇 |
1977年 | 2篇 |
1976年 | 2篇 |
1972年 | 3篇 |
1907年 | 1篇 |
排序方式: 共有1396条查询结果,搜索用时 0 毫秒
1.
Activated carbon production from almond shells using phosphoric acid activation agent was achieved by applying both conventional heating and microwave heating in succession. The morphology and surface properties of activated carbon were studied using thermogravimetric and differential gravimetric analysis, Fourier-transform infrared spectroscopy, scanning electron microscopy, and Brunauer–Emmett–Teller analysis. A surface area of 1128 m2/g was achieved by optimizing the microwave power (500?W), microwave application time (15?minutes), conventional heating time (45?minutes), conventional heating temperature (500?°C), and the phosphoric acid:sample ratio (0.7:1). An adsorption capacity of methylene blue of 148?mg/g and an iodine value of 791?mg/g was obtained for the prepared activated carbon. 相似文献
2.
In [5] Phillips proved that one can obtain the additive group of any nonstandard model *? of the ring ? of integers by using a linear mod 1 function h : F ?, where F is the α-dimensional vector space over ? when α is the cardinality of *?. In this connection it arises the question whether there are linear mod 1 functions which are neither addition nor quasi-linear. We prove that this is the case. 相似文献
3.
Marco Sangermano Mehmet Atilla Tasdelen Yusuf Yagci 《Journal of polymer science. Part A, Polymer chemistry》2007,45(21):4914-4920
Photoinitiated cationic polymerization of mono‐ and bifunctional epoxy monomers, namely cyclohexeneoxide (CHO), 4‐epoxycyclohexylmethyl‐3′,4′‐epoxycyclohexanecarboxylate (EEC), respectively by using sulphonium salts in the presence of hydroxylbutyl vinyl ether (HBVE) was studied. The real‐time FTIR spectroscopic, gel content determination, and thermal characterization studies revealed that both hydroxyl and vinyl ether functionalities of HBVE take part in the polymerization. During the polymerization, HBVE has the ability to react via both active chain end (ACE) and activated monomer mechanisms through its hydroxyl and vinyl ether functionalities, respectively. Thus, more efficient curing was observed with the addition of HBVE into EEC‐containing formulations. It was also demonstrated that HBVE is effective in facilitating the photoinduced crosslinking of monofunctional epoxy monomer, CHO in the absence of a conventional crosslinker. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4914–4920, 2007 相似文献
4.
Celik Tarimci Anda? Karamustafa Kutalmi? Güven Mehmet Kabak Akgül Ye?ilada 《Analytical sciences》2003,19(9):1347-1348
The crystal structure of 1-[3-(3,4-dimethoxyphenyl)-2-propenoyl]pyrrolidine (C15H19NO3) (I) has been determined by X-ray analysis. It crystallizes orthorhombic space group Pbca with a = 24.295(3), b = 15.086(3), c = 7.552(3)A, V = 2768(1)A3, Z = 8, Dcalc = 1.254 g/cm3, mu = (Mo K(alpha)) = 0.87 cm(-1). The title compound has analgesic activity of cycloaliphatic amine part. The molecule is deviated from planar configuration. 相似文献
5.
The high-speed response properties of resonant cavity enhanced (RCE) photodetectors have been investigated. The limitations on the high-speed performance of photodiodes and the advantages of RCE-detection are discussed. Transient response of heterojunction photodiodes under pulsed optical illumination has been simulated using the method described in Part I. Results on conventional AlGaAs/GaAs and RCE GaAs/InGaAs heterojunction p-i-n photodiodes are presented. For small area detectors, almost 50% bandwidth improvement along with a two-fold increase in efficiency is predicted for RCE devices over optimized conventional photodiodes. A nearly three-fold enhancement in the bandwidth-efficiency product was shown 相似文献
6.
Bünyamin Demir Vakif Dzhafarov ?ahin Koçak Mehmet Üreyen 《Journal of Mathematical Analysis and Applications》2007,332(1):735-740
We give an iterated function system (IFS) on the plane with the circle as attractor. In doing this, we also give a sufficient condition for radially contracting functions on the plane (or on Rn) to be a contraction. A counterexample shows that radial contractiveness is not enough to be a contraction. 相似文献
7.
The centrosymmetric title compound, [Cd2{CH3OC6H4P(OC5H9)S2}4], features an eight‐membered [? Cd? S? P? S? ]2 ring owing to the presence of bridging dithiolate ligands. Tetrahedral coordination geometries for cadmium are completed by chelating ligands. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
8.
Antimicrobial activity studies of the binuclear metal complexes derived from tridentate Schiff base ligands 总被引:1,自引:0,他引:1
Tümer Mehmet Köksal Hüseyin Sener M. Kasim Serin Selahattin 《Transition Metal Chemistry》1999,24(4):414-420
Three novel tridentate Schiff base ligands derived fromthe 3-hydroxysalicylaldehyde (H2L1), 4-hydroxysalicylaldehyde (H2L2) and 5-bromosalicylaldehyde (H2L3) with a new amine N-(pyridyl)-2-hydroxy-3-methoxy-5-aminobenzylamine (2) have been prepared. The ligands and their metal complexes have been characterized by elemental analyses, conductivity and magnetic susceptibility measurements, i.r., electronic absorption and 1H and 13C n.m.r. spectroscopy. All complexes are binuclear and, in some, the H2O molecules are coordinated to the metal ion. Antimicrobial activities of the ligands and their complexes have been tested against to the Bacillus subtilis IMG 22 (bacteria), Micrococcus luteus LA 2971 (bacteria) Saccharamyces cerevisiae WET 136 (yeast), and Candida albicans CCM 314 (yeast). Thermal properties of all complexes have been studied by t.g. and d.t.a techniques. 相似文献
9.
Dai H Choe WS Thai CK Sarikaya M Traxler BA Baneyx F Schwartz DT 《Journal of the American Chemical Society》2005,127(44):15637-15643
We show that a protein with no intrinsic inorganic synthesis activity can be endowed with the ability to control the formation of inorganic nanostructures under thermodynamically unfavorable (nonequilibrium) conditions, reproducing a key feature of biological hard-tissue growth and assembly. The nonequilibrium synthesis of Cu(2)O nanoparticles is accomplished using an engineered derivative of the DNA-binding protein TraI in a room-temperature precursor electrolyte. The functional TraI derivative (TraIi1753::CN225) is engineered to possess a cysteine-constrained 12-residue Cu(2)O binding sequence, designated CN225, that is inserted into a permissive site in TraI. When TraIi1753::CN225 is included in the precursor electrolyte, stable Cu(2)O nanoparticles form, even though the concentrations of [Cu(+)] and [OH(-)] are at 5% of the solubility product (K(sp,Cu2O)). Negative control experiments verify that Cu(2)O formation is controlled by inclusion of the CN225 binding sequence. Transmission electron microscopy and electron diffraction reveal a core-shell structure for the nonequilibrium nanoparticles: a 2 nm Cu(2)O core is surrounded by an adsorbed protein shell. Quantitative protein adsorption studies show that the unexpected stability of Cu(2)O is imparted by the nanomolar surface binding affinity of TraIi1753::CN225 for Cu(2)O (K(d) = 1.2 x 10(-)(8) M), which provides favorable interfacial energetics (-45 kJ/mol) for the core-shell configuration. The protein shell retains the DNA-binding traits of TraI, as evidenced by the spontaneous organization of nanoparticles onto circular double-stranded DNA. 相似文献
10.