全文获取类型
收费全文 | 6260篇 |
免费 | 1086篇 |
国内免费 | 1032篇 |
专业分类
化学 | 4825篇 |
晶体学 | 145篇 |
力学 | 329篇 |
综合类 | 87篇 |
数学 | 735篇 |
物理学 | 2257篇 |
出版年
2024年 | 12篇 |
2023年 | 174篇 |
2022年 | 215篇 |
2021年 | 299篇 |
2020年 | 374篇 |
2019年 | 348篇 |
2018年 | 275篇 |
2017年 | 304篇 |
2016年 | 365篇 |
2015年 | 382篇 |
2014年 | 475篇 |
2013年 | 561篇 |
2012年 | 611篇 |
2011年 | 599篇 |
2010年 | 443篇 |
2009年 | 417篇 |
2008年 | 432篇 |
2007年 | 376篇 |
2006年 | 340篇 |
2005年 | 241篇 |
2004年 | 210篇 |
2003年 | 126篇 |
2002年 | 182篇 |
2001年 | 148篇 |
2000年 | 116篇 |
1999年 | 83篇 |
1998年 | 60篇 |
1997年 | 32篇 |
1996年 | 28篇 |
1995年 | 20篇 |
1994年 | 28篇 |
1993年 | 14篇 |
1992年 | 9篇 |
1991年 | 19篇 |
1990年 | 10篇 |
1989年 | 5篇 |
1988年 | 4篇 |
1987年 | 5篇 |
1986年 | 2篇 |
1985年 | 7篇 |
1984年 | 3篇 |
1983年 | 3篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1977年 | 3篇 |
1975年 | 1篇 |
1974年 | 4篇 |
1971年 | 2篇 |
1959年 | 2篇 |
1936年 | 1篇 |
排序方式: 共有8378条查询结果,搜索用时 31 毫秒
991.
电流控阈技术及二值I~2L施密特电路设计黄瑞祥,杭国强(杭州大学电子工程系杭州310028)在数字电路中,以往对施密特电路的分析与研究大多局限于用电压信号来表示逻辑值的电路,例如TTL、CMOS、ECL等电路[1-3].然而,对于以电流为信号的电流型?.. 相似文献
992.
993.
994.
Summary Cobalt(II) can be determined in 0.1 mol/l Na3citrate + 0.1 mol/l NH4Cl + 0.08% dimethylglyoxime as supporting electrolyte in the presence of a 50 000-fold excess of zinc by differential pulse polarography. The limit of determination is 4.2×10–5 mol/l Co (2.5 mg/l). Linear calibration curves are obtained within the range of 1×10–7 to 5×10–6 mol/l cobalt without zinc and in the presence of 5×10–3 mol/l Zn. The analytical method developed is suitable for the determination of cobalt in zinc plant solutions.
Cobaltbestimmung in Gegenwart hoher Zinkkonzentrationen mit Hilfe der Differential-Puls-Polarographie相似文献
995.
Rui J. P. de Figueiredo 《Journal of Approximation Theory》1977,19(4):332-360
As an extension of the notion of an L-g spline, three mathematical structures called LM-g splines of types I, II, and III are introduced. Each is defined in terms of two differential operators the coefficients aj, J = 0,…, n − 1, and bi, I = 0,…, m, are sufficiently smooth; and bm is bounded away from zero on [0, T]. Each of the above types of splines is the solution of an optimization problem more general than the one used in the definition of the L-g spline and hence it is recognized as an entity which is distinct from and more general mathematically than the L-g spline. The LM-g splines introduced here reduce to an L-g spline in the special case in which m = 0 and b0 = constant ≠ 0. After the existence and uniqueness conditions, characterization, and best approximation properties for the proposed splines are obtained in an appropriate reproducing kernel Hilbert space framework, their usefulness in extending the range of applicability of spline theory to problems in estimation, optimal control, and digital signal processing are indicated. Also, as an extension of recent results in the generalized spline literature, state variable models for the LM-g splines introduced here are exhibited, based on which existing least squares algorithms can be used for the recursive calculation of these splines from the data. 相似文献
996.
Miscibility in blends of three styrene-butadiene-styrene and one styrene-isoprene-styrene triblock copolymers containing 28%, 30%, 48%, and 14% by weight of polystyrene, respectively, with poly(vinyl methyl ether) (PVME) were investigated by FTIR spectroscopy and differential scanning calorimetry (DSC). It was found from the optical clarity and the glass transition temperature behavior that the blends show miscibility for each kind of triblock copolymers below a certain concentration of PVME. The concentration range to show miscibility becomes wider as the polystyrene content and molecular weight of PS segment in the triblock copolymers increase. From the FTIR results, the relative peak intensity of the 1100 cm-1 region due to COCH3 band of PVME and peak position of 698 cm-1 region due to phenyl ring are sensitive to the miscibility of SBS(SIS)/PVME blends. The results show that the miscibility in SBS(SIS)/PVME blends is greatly affected by the composition of the copolymers and the polystyrene content in the triblock copolymers. Molecular weights of polystyrene segments have also affected the miscibility of the blends. ©1995 John Wiley & Sons, Inc. 相似文献
997.
Hua Fang Mei Juan Fang Rui Zao Yi Yu Fen Zhao 《Journal of chemical crystallography》2008,38(10):761-764
Abstract The title compound, C14H23O5P, was synthesized by the reaction of 4-methoxybenzaldehyde and diisopropyl phosphite. Its structure was determined with X-ray
crystallographic, NMR, MS, and elemental analysis (EA) techniques. The crystal belongs to monoclinic, space group P 21/n with the following crystallographic parameters: a = 10.529 (2) ?, b = 8.424 (2) ?, c = 19.448 (4) ?, α = 90°, β = 105.2 (3)°, γ = 90°, μ = 0.180 mm−1, V = 1664.1 (6) ?3, Z = 4, Dx = 1.207 mg/mm3, F (000) = 648, T = 293 (2) K, 2.00° ≤ θ ≤ 25.50°. The final residual factor is 0.049 for 1933 reflections with I > 2σ (I). Crystal packing is stabilized by interatomic hydrogen bond interactions between the doubly bonded phosphoryl O atom and
the hydroxyl H atom which link the molecules into chains along the [011] plane of the unit cell.
Index Abstract The title compound, diisopropyl hydroxy(4-methoxyphenyl)methylphosphonate, was synthesized by the reaction of 4-methoxybenzaldehyde
and diisopropyl phosphite. Its structure was determined with X-ray crystallographic, NMR, MS, and elemental analysis (EA)
techniques. Crystal packing is stabilized by interatomic hydrogen bond interactions between the doubly bonded phosphoryl O
atom and the hydroxyl H atom which link the molecules into chains along the [011] plane of the unit cell.
相似文献
998.
Rui Miguel Saramago 《Proceedings of the American Mathematical Society》2008,136(8):2699-2709
We use Dieudonné theory for periodically graded Hopf rings to determine the Dieudonné ring structure of the -graded Morava -theory , with an odd prime, when applied to the -spectrum (and to ). We also expand these results in order to accomodate the case of the full Morava -theory .
999.
Copolymers of phosphafluorenes are obtained through Suzuki copolymerization. The phosphorus-containing copolymers show unique optical, electrochemical, and optoelectronic properties. Blue and white electroluminescence can be observed, depending on the modifications of the phosphorus atoms. It is the first time that conjugated polymers containing phosphafluorene have been prepared and used in PLEDs. Phosphafluorenes are new building blocks for conjugated oligomers and polymers. 相似文献
1000.
Vale N Matos J Moreira R Gomes P 《Journal of the American Society for Mass Spectrometry》2008,19(10):1476-1490
Electrospray ionization-ion trap mass spectrometry (ESI-MS) of imidazolidin-4-one peptidomimetic derivatives of the antimalarial
drug primaquine (PQ) is reported. These compounds contain the imidazolidin-4-one moiety either at the N- or the C-terminal of a dipeptide backbone, thus respectively mimicking PQ-Amino Acid-Proline (PQAAPro) and PQProAA derivatives of
PQ. Both the peptidomimetics and precursors previously developed by us are promising drug candidates, as they were found to
be active against rodent Plasmodium berghei malaria and Pneumocystis carinii pneumonia. Collision-induced dissociation (CID) and tandem-mass spectra (MS) of the title compounds, and fragmentation pathways
thereof, led to the following findings: (1) CID patterns present some parallelism with the reactivity towards hydrolysis previously
found for the same or related compounds; (2) a positional shift of the imidazolidin-4-one ring is reflected on both degree
and pathways of fragmentation, which makes tandem-MS a key tool for differentiation of imidazolidin-4-one isomers; (3) the
major MS/MS fragmentation of PQProAA mimetics involves release of a neutral diketopiperazine (DKP), in parallel to the “diketopiperazine
pathway” described in tandem-MS studies of oligopeptides; (4) the relative abundance of a major fragment in tandem-MS spectra
is inversely correlated with the size of the N-terminal AA in PQProAA mimetics. Overall, this work embodies an original and valuable contribution towards a deeper insight
into the molecular properties of novel antimalarials, which can be viewed as representative of both the 8-aminoquinoline and,
especially, the imidazolidin-4-one structural classes. 相似文献