全文获取类型
收费全文 | 18898篇 |
免费 | 1612篇 |
国内免费 | 846篇 |
专业分类
电工技术 | 860篇 |
技术理论 | 1篇 |
综合类 | 890篇 |
化学工业 | 3233篇 |
金属工艺 | 1026篇 |
机械仪表 | 929篇 |
建筑科学 | 1144篇 |
矿业工程 | 296篇 |
能源动力 | 591篇 |
轻工业 | 1880篇 |
水利工程 | 349篇 |
石油天然气 | 563篇 |
武器工业 | 106篇 |
无线电 | 1851篇 |
一般工业技术 | 2542篇 |
冶金工业 | 1909篇 |
原子能技术 | 199篇 |
自动化技术 | 2987篇 |
出版年
2024年 | 109篇 |
2023年 | 342篇 |
2022年 | 856篇 |
2021年 | 1083篇 |
2020年 | 708篇 |
2019年 | 593篇 |
2018年 | 611篇 |
2017年 | 714篇 |
2016年 | 656篇 |
2015年 | 790篇 |
2014年 | 1019篇 |
2013年 | 1204篇 |
2012年 | 1304篇 |
2011年 | 1392篇 |
2010年 | 1149篇 |
2009年 | 1090篇 |
2008年 | 1006篇 |
2007年 | 894篇 |
2006年 | 815篇 |
2005年 | 655篇 |
2004年 | 477篇 |
2003年 | 394篇 |
2002年 | 364篇 |
2001年 | 331篇 |
2000年 | 270篇 |
1999年 | 264篇 |
1998年 | 505篇 |
1997年 | 408篇 |
1996年 | 271篇 |
1995年 | 175篇 |
1994年 | 142篇 |
1993年 | 137篇 |
1992年 | 60篇 |
1991年 | 46篇 |
1990年 | 61篇 |
1989年 | 40篇 |
1988年 | 35篇 |
1987年 | 34篇 |
1986年 | 25篇 |
1985年 | 35篇 |
1984年 | 28篇 |
1983年 | 27篇 |
1982年 | 23篇 |
1981年 | 42篇 |
1980年 | 26篇 |
1979年 | 16篇 |
1978年 | 16篇 |
1977年 | 29篇 |
1976年 | 34篇 |
1975年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
51.
Emilio Marengo Valentina Longo Elisa Robotti Marco Bobba Fabio Gosetti Orfeo Zerbinati Silvana Di Martino 《应用聚合物科学杂志》2008,109(6):3975-3982
Principal component regression (PCR), partial least squares (PLS), StepWise ordinary least squares regression (OLS), and back‐propagation artificial neural network (BP‐ANN) are applied here for the determination of the propylene concentration of a set of 83 production samples of ethylene–propylene copolymers from their infrared spectra. The set of available samples was split into (a) a training set, for models calculation; (b) a test set, for selecting the correct number of latent variables in PCR and PLS and the end point of the training phase of BP‐ANN; (c) a production set, for evaluating the predictive ability of the models. The predictive ability of the models is thus evaluated by genuine predictions. The model obtained by StepWise OLS turned out to be the best one, both in fitting and prediction. The study of the breakdown number of samples to be included in the training set showed that at least 52 experiments are necessary to build a reliable and predictive calibration model. It can be concluded that FTIR spectroscopy and OLS can be properly employed for monitoring the synthesis or the final product of ethylene–propylene copolymers, by predicting the concentration of propylene directly along the process line. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 相似文献
52.
53.
A novel monomer containing pyridylazo-2-naphthoxyl group, 1-(1-(4-vinylbenzyloxy)naphthalen-2-yl)-2-(pyridin-2-yl)diazene (VBNPA), was successfully synthesized and copolymerized with styrene (St) in N,N-dimethyl formamide (DMF) via reversible addition–fragmentation chain transfer (RAFT) polymerization using 2-cyanoprop-2-yl-1-dithionaphthalate (CPDN) as RAFT agent. The polymerization behavior exhibited “living”/controlled characters. The obtained copolymer, poly(St-co-VBNPA), with pre-determinable molecular weight and narrow molecular weight distribution can be used as a carrier in metal ion detection and analysis via pre-concentration technique. The copolymer–metal ion (copper (Cu) and europium (Eu)) complexes were prepared and characterized. 相似文献
54.
This paper reports off-lattice Monte Carlo simulations of highly-branched comb homopolymers weakly adsorbed on a flat, featureless surface showing only covolume and dispersion interactions with the adsorbate. A minimal coarse-grained model, described by hard spheres connected by harmonic springs, was employed. The interaction energy of the adsorbed combs and linear chains is first discussed as a function of the molecular mass and of the number of beads in contact with the surface. The molecular size is then investigated as a function of backbone length and branching density at a fixed arm size. The apparent swelling exponents of the adsorbed combs are larger than those of the corresponding linear chains, and much larger than that of the free molecules. This result indicates a surface-induced stiffening of the comb backbone, further studied through the persistence length lpers. It is found that lpers increases upon adsorption over the free-molecule value, more so the larger is the branching density. Finally, the thickness of the adsorbed layer, the surface-induced molecular anisotropy and the molecular aspect ratio are investigated as a function of branching density and molecular mass. 相似文献
55.
56.
A new approach to study ergodicity of filtering processes is presented. It is based on the vanishing discount approach to discounted functional of filtering process. We show that limit superior of the Cesaro averages of the functionals is the same for all initial conditions from which the uniqueness of invariant measures of filtering processes follows. The approach is based on certain assumption for which we provide a sufficient condition using concavity arguments. In addition we show the existence of solutions to the Poisson equation corresponding to filtering process with concave functional. The assumptions are then extended to the controlled case and using similar concave arguments we obtain the existence of solutions to the Bellman equation corresponding to partially observed average cost per unit time problem. 相似文献
57.
58.
A Di Lieto G De Rosa G Albano F Gallo M Pontillo R Micalef A Colucci A Paladini 《Canadian Metallurgical Quarterly》1996,23(4):220-228
Clinical and pathological changes of the mammary gland have been studied in 64 women affected by symptomatic Benign Breast Disease (BBD) coexisting with endometriosis or uterine leiomyomata. These patients were rendered hypoestrogenic by subcutaneous administration of the LH-RH analogue Goserelin depot [D-ser (tBu)6 Aza-Gly10-GnRH (ICI118630)] performed every 28 days, for six months. They were evaluated clinically and ultrasonographically before and after treatment to find possible changes of BBD as well as of endometriosis or uterine leiomyomata. Mammary biopsies were performed before and after treatment in all the patients to study the changes of EGF-R expression. Results showed that clinical improvement is accompanied with a reduction of EGF-R expression. 相似文献
59.
关系数据库在专家系统中的应用 总被引:6,自引:0,他引:6
在传统的专家系统中,对推理机工作过程的控制是程序实现的。本文介绍了一个用数据库技术引导推理过程的专家系统-精神分裂症诊断专家系统(ESSD)的推理控制策略。在这个专家系统中,作者将有关推理过程的控制信息用关系数据库技术进行存储和管理,达到了将控制策略数据化的目的。将数据库技术引入到专家系统的推进控制机制中可以使控制策略比较容易调整,且而可以大大压缩程序篇幅,显著提高系统运行效率,为专家系统的结构设 相似文献
60.
The complete mechanism by which pathogenic mtDNA mutations cause cellular pathophysiology and in some cases cell death is unclear. Oxidant stress is especially toxic to excitable nerve and muscle cells, cells that are often affected in mitochondrial disease. The sensitivity of cells bearing the LHON, MELAS, and MERRF mutations to oxidant stress was determined. All were significantly more sensitive to H2O2 exposure than their nonmutant cybrid controls, the order of sensitivity was MELAS > LHON > MERRF > controls. Depletion of Ca2+ from the medium protected all cell lines from oxidant stress, consistent with the hypothesis that death induced by oxidant stress is Ca(2+)-dependent. A potential downstream target of Ca2+ is the mitochondrial permeability transition, MPT, which is inhibited by cyclosporin A. Treatment of MELAS, LHON, and MERRF cells with cyclosporin A caused significant rescue from oxidant exposure, and in each case significantly greater rescue of mutant than control cells. The pronounced oxidant-sensitivity of mutant cells, and their protection by Ca2+ depletion and CsA, has potential implications for both the pathophysiological mechanism and therapy of these mitochondrial genetic diseases. 相似文献