全文获取类型
收费全文 | 1561篇 |
免费 | 68篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 28篇 |
化学工业 | 539篇 |
金属工艺 | 12篇 |
机械仪表 | 41篇 |
建筑科学 | 54篇 |
能源动力 | 52篇 |
轻工业 | 189篇 |
水利工程 | 7篇 |
石油天然气 | 2篇 |
武器工业 | 1篇 |
无线电 | 121篇 |
一般工业技术 | 218篇 |
冶金工业 | 40篇 |
原子能技术 | 17篇 |
自动化技术 | 309篇 |
出版年
2024年 | 3篇 |
2023年 | 11篇 |
2022年 | 95篇 |
2021年 | 87篇 |
2020年 | 39篇 |
2019年 | 41篇 |
2018年 | 45篇 |
2017年 | 28篇 |
2016年 | 45篇 |
2015年 | 43篇 |
2014年 | 65篇 |
2013年 | 113篇 |
2012年 | 108篇 |
2011年 | 104篇 |
2010年 | 88篇 |
2009年 | 68篇 |
2008年 | 68篇 |
2007年 | 80篇 |
2006年 | 63篇 |
2005年 | 50篇 |
2004年 | 47篇 |
2003年 | 44篇 |
2002年 | 36篇 |
2001年 | 22篇 |
2000年 | 20篇 |
1999年 | 24篇 |
1998年 | 18篇 |
1997年 | 20篇 |
1996年 | 19篇 |
1995年 | 11篇 |
1994年 | 19篇 |
1993年 | 12篇 |
1992年 | 10篇 |
1991年 | 3篇 |
1990年 | 5篇 |
1989年 | 6篇 |
1988年 | 4篇 |
1987年 | 5篇 |
1986年 | 4篇 |
1984年 | 8篇 |
1983年 | 5篇 |
1982年 | 7篇 |
1980年 | 6篇 |
1979年 | 3篇 |
1978年 | 5篇 |
1977年 | 4篇 |
1973年 | 2篇 |
1971年 | 3篇 |
1967年 | 2篇 |
1966年 | 2篇 |
排序方式: 共有1630条查询结果,搜索用时 0 毫秒
91.
Cascone MG Lazzeri L Sparvoli E Scatena M Serino LP Danti S 《Journal of materials science. Materials in medicine》2004,15(12):1309-1313
Poly(vinyl alcohol) hydrogels prepared by freeze-thawing procedure represent synthetic systems widely investigated as non-biodegradable scaffolds for tissue regeneration. In order to improve the biocompatibility properties of pure poly(vinyl alcohol) (PVA) hydrogels, blends of PVA with different biological macromolecules, such hyaluronic acid, dextran, and gelatin were prepared and used to produce bioartificial hydrogels. The porosity characteristics of these hydrogels were investigated by scanning electron microscopy and mercury intrusion porosimetry. The morphology of bioartificial hydrogels was evaluated and compared with that of pure PVA hydrogels. In particular the effect exerted by each biological component on pore size and distribution was investigated. The obtained results indicate that when a natural macromolecule is added to PVA the internal structure of the material changes. A small amount of biopolymer induces the structural elements of PVA matrix to take on a well evident lamellar appearance and an apparent preferential orientation. Comparing the results of SEM and mercury intrusion porosimetry it was concluded that hydrogels containing 20% of biological component have the most regular structure and at the same time the lowest total porosity. On the contrary samples with the highest content of natural polymer (40%) show the less regular structure and the highest total porosity. 相似文献
92.
Testi D Quadrani P Petrone M Zannoni C Fontana F Viceconti M 《Computer methods and programs in biomedicine》2004,75(3):213-220
This work is aimed at developing an innovative simulation environment supporting and improving the design of standard joint implants (JPD integrated design environment (JIDE)). The conceptual workflow starts from the design of a new implant, by using conventional CAD programmes and completes with the generation of a report that summarises the goodness for a new implant against a database of human bone anatomies. For each dataset in the database, the JPD application calculates a set of quantitative indicators that will support the designer in the evaluation of its design on a statistical basis. The resulting system is thus directed to prostheses manufacturers and addresses a market segment that appears to have a steady growth in the future. 相似文献
93.
In this paper a methodological approach is proposed to validate mechanistic modeling for proton binding onto active sites of mineral and soil samples by reducing the uncertainty and arbitrariness of model schematization. This approach is based on the quantitative formulation (X-ray calibration method) of a simulating mineral mixture (SMM) accounting for the main mineral phases in the soil (quartz, goethite, hematite, muscovite, clinochlore). Mineral and organic contributions were separated by comparing titration curves of river sediment and SMM. Specific mineral contributions to the acid properties of SMM were separated by comparing titration models of SMM and single minerals. Different nonelectrostatic models were used for titrations of SMM and single minerals: two-site/three-KH models (one amphoteric plus one monoprotic site) for clay minerals and SMM; one-site/two-KH models (one amphoteric site) for goethite and hematite; and a one-site/one-KH model (one monoprotic site) for quartz. Crossed-comparisons of titration models allow for identifying and quantifying the specific contributions of the distinct edge hydroxyl groups of iron oxides, clay minerals, and quartz in the different pH ranges. In particularthe amphoteric sites of aluminosilicates mainly contribute in the acid-neutral pH range, the amphoteric sites of iron oxides take part in the neutral-basic range, and finally the monoprotic edge hydroxyl groups of quartz react in the upper basic region of pH. The good simulation of the acid-base properties of SMM (according to single mineral titration models and quantitative composition by X-ray) confirms both model schematization and SMM formulation. Speciation diagrams of the active sites of the different mineral components (aluminosilicates, iron oxides, and quartz) were obtained by implementing the database of a dedicated software with the apparent equilibrium constants regressed by titration modeling of single minerals. 相似文献
94.
Smith JT Wright SM Cross MA Monte L Kudelsky AV Saxén R Vakulovsky SM Timms DN 《Environmental science & technology》2004,38(3):850-857
Atmospheric nuclear weapons explosions and large-scale nuclear accidents may contaminate large areas of land with the long-lived radionuclides 137Cs and 90Sr. The mobility and bioavailability of these radionuclides in the environment is dependent primarily on soil characteristics and changes significantly over time after fallout (1-4). Radioisotope concentrations in different rivers and at different times after fallout vary over 2-3 orders of magnitude. Many previous studies have concentrated on the interactions of radiocesium and radiostrontium with various environmental components, but there are currently no operative models fortheirtransport over large spatial areas. We collected time-series measurements of 90Sr and 137Cs in 25 major European and Asian rivers and (using digital data sets with global coverage) determined characteristics of each of the rivers' catchments. This work has established, for the first time, a quantitative link between riverine transport of these radioisotopes and catchment and soil characteristics at a global scale. A generalized predictive model accounting for time changes in river concentrations and variation in catchment characteristics is developed. This can be used to predict the long-term riverine transport of these radiologically important radionuclides following any large-scale nuclear incident in North America, Europe, or (European and Asian) Russia. 相似文献
95.
Bedini Luigi Bramanti Mauro Denoth F. 《IEEE transactions on bio-medical engineering》1980,(11):623-630
In this paper the electromagnetic interaction between a resonator and a lossy dielectric body is examined by means of a simple model suitable for computer simulation; the body was assumed to have a revolution form and the resonator was electromagnetic coupled to the body by its inductive element constituted by a planar circular or spiral coil. On the basis of the model a computer program was derived which allows a simple numerical evaluation of the variation in the resonant frequency caused by the interaction mentioned above. 相似文献
96.
97.
Nassimbeni LR 《Accounts of chemical research》2003,36(8):631-637
The macro properties of crystalline inclusion compounds depend on their structures. Their thermal stabilities are a function of the strength and the directionality of the various nonbonded interactions occurring in the host-guest assembly. Their lattice energies, as measured by the method of atom-atom potentials, correlate with the thermodynamics of the guest-release reactions and the selectivity that a given host displays for a particular guest. The kinetics of solid-host:vapor-guest reactions and of guest exchange are important in our understanding of catalytic processes. Crystal engineering, in which materials of predetermined properties may be synthesized, is still at the empirical stage. 相似文献
98.
99.
De Luca S Ragone R Bracco C Digilio G Aloj L Tesauro D Saviano M Pedone C Morelli G 《Chembiochem : a European journal of chemical biology》2003,4(11):1176-1187
A cyclic CCK8 analogue, cyclo(29,34)[Dpr(29),Lys(34)]-CCK8 (Dpr=L-2,3-diaminopropionic acid), has been designed on the basis of the NMR structure of the bimolecular complex between the N-terminal fragment of the CCK(A) receptor and its natural ligand CCK8. The conformational features of cyclo(29,34)[Dpr(29),Lys(34)]-CCK8 have been determined by NMR spectroscopy in aqueous solution and in water containing DPC-d(38) micelles (DPC=dodecylphosphocholine). The structure of the cyclic peptide in aqueous solution is found to be in a relaxed conformation, with the backbone and Dpr29 side chain atoms making a planar ring and the N-terminal tripeptide extending approximately along the plane of this ring. In DPC/water, the cyclic peptide adopts a "boat-shaped" conformation, which is more compact than that found in aqueous solution. The cyclic constraint between the Dpr29 side chain and the CCK8 carboxyl terminus (Lys34) introduces a restriction in the backbone conformational freedom. However, the interaction of cyclo(29,34)[Dpr(29),Lys(34)]-CCK8 with the micelles still plays an important role in the stabilisation of the bioactive conformation. A careful comparison of the NMR structure of the cyclic peptide in a DPC micelle aqueous solution with the structure of the rationally designed model underlines that the turn-like conformation in the Trp30-Met31 region is preserved, such that the Trp30 and Met31 side chains can adopt the proper spatial orientation to interact with the CCK(A) receptor. The binding properties of cyclo(29,34)[Dpr(29),Lys(34)]-CCK8 to the N-terminal receptor fragment have been investigated by fluorescence spectroscopy in a micellar environment. Estimates of the apparent dissociation constant, K(d), were in the range of 70-150 nM, with a mean value of 120+/-27 nM. Preliminary nuclear medicine studies on cell lines transfected with the CCK(A) receptor indicate that the sulfated-Tyr derivative of cyclo(29,34)[Dpr(29),Lys(34)]-CCK8 displaces the natural ligand with an IC(50) value of 15 microM. 相似文献
100.
Bassarello C Cimino P Bifulco G Boger DL Smith JA Chazin WJ Gomez-Paloma L 《Chembiochem : a European journal of chemical biology》2003,4(11):1188-1193
We report the NMR solution structure of (+)-CPI-indole (CPI, 1,2,8,8a-tetrahydrocyclopropa[c]pyrrolo[3,2-e]indol-4(5H)-one), an agent belonging to the CC-1065/duocarmycin family of antitumor compounds. This (+)-CPI-indole structure is covalently bound to d(G(1)ACTAATTGTC(11))-d(G(12)TCAATTAGTC(22)), a synthetic DNA duplex containing a high-affinity binding site. The three-dimensional structure has been determined by several cycles of restrained molecular dynamics calculations with a total of 563 NMR-derived constraints, both in vacuo and by using the generalized Born solvent continuum model. In-depth analysis of the structure of this ligand-DNA complex led to a detailed knowledge of the bound state conformation of the CPI-indole, the most simplified agent related to CC-1065 and duocarmycins, the parent members of a family of extremely potent antitumor compounds. Comparison of the CPI-indole bound conformation with those previously found for (+)-duocarmycin SA (DSA), its unnatural enantiomer (-)-DSA, and the demethoxylated analogue (+)-DSI in their DNA complexes provided additional evidence of the tight correlation between the catalytic effect exerted by DNA on the alkylation reaction and the extent of angular twist between the two planar heteroaromatic subunits of these agents. Additionally, comparison of the structural features of the DNA-bound state of a "naked" ligand, such as CPI-indole, with those of various other duocarmycin agents provided useful information for the interpretation of the observed effects on chemical reactivity of the different substitution patterns at the hemispheres of these types of complex. 相似文献