全文获取类型
收费全文 | 122823篇 |
免费 | 9785篇 |
国内免费 | 5524篇 |
专业分类
电工技术 | 6237篇 |
技术理论 | 1篇 |
综合类 | 9104篇 |
化学工业 | 21259篇 |
金属工艺 | 5928篇 |
机械仪表 | 7122篇 |
建筑科学 | 8821篇 |
矿业工程 | 2347篇 |
能源动力 | 4078篇 |
轻工业 | 10114篇 |
水利工程 | 2207篇 |
石油天然气 | 4957篇 |
武器工业 | 767篇 |
无线电 | 14420篇 |
一般工业技术 | 14985篇 |
冶金工业 | 6147篇 |
原子能技术 | 1560篇 |
自动化技术 | 18078篇 |
出版年
2024年 | 458篇 |
2023年 | 1573篇 |
2022年 | 3015篇 |
2021年 | 4316篇 |
2020年 | 3406篇 |
2019年 | 3125篇 |
2018年 | 3441篇 |
2017年 | 3730篇 |
2016年 | 3603篇 |
2015年 | 4243篇 |
2014年 | 5779篇 |
2013年 | 7578篇 |
2012年 | 7987篇 |
2011年 | 8501篇 |
2010年 | 7566篇 |
2009年 | 7419篇 |
2008年 | 7200篇 |
2007年 | 6920篇 |
2006年 | 6778篇 |
2005年 | 5722篇 |
2004年 | 4525篇 |
2003年 | 4058篇 |
2002年 | 4579篇 |
2001年 | 3966篇 |
2000年 | 3060篇 |
1999年 | 2557篇 |
1998年 | 2244篇 |
1997年 | 1806篇 |
1996年 | 1672篇 |
1995年 | 1379篇 |
1994年 | 1071篇 |
1993年 | 902篇 |
1992年 | 661篇 |
1991年 | 508篇 |
1990年 | 474篇 |
1989年 | 334篇 |
1988年 | 301篇 |
1987年 | 223篇 |
1986年 | 179篇 |
1985年 | 164篇 |
1984年 | 135篇 |
1983年 | 129篇 |
1982年 | 109篇 |
1981年 | 91篇 |
1980年 | 78篇 |
1979年 | 60篇 |
1978年 | 50篇 |
1977年 | 64篇 |
1976年 | 103篇 |
1974年 | 46篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
121.
122.
123.
把由非谐振环和凸面全反射镜构成的自滤波非稳腔应用于撞脉冲锁模Nd:YAG激光器,改善了光束的空间质量和输出稳定性,获得发散角为2倍衍射极限,能量50mJ,脉宽10ps的锁模脉冲,并与未加滤波小孔的CPM非稳腔的输出性能进行实验比较。, 相似文献
124.
煤气吹扫时惰性气体抑爆用量的优选 总被引:1,自引:0,他引:1
运用惰性气体消防抑爆理论,采用数学积分法计算出吹扫煤气设施时抑爆所需最少惰性气体需要量. 相似文献
125.
Hong Lin H. Nayeb-Hashemi R. M. Pelloux 《Fatigue & Fracture of Engineering Materials & Structures》1993,16(7):723-742
A new multiaxial fatigue damage model for orthotropic materials is proposed based on the strain vector. Six material constants are included in the model. These material constants represent the dependence of fatigue resistance on material orientation, and they can be obtained by conducting strain-controlled uniaxial fatigue tests along the three principal orthotropic directions of an orthotropic material. The model can also be transformed in new coordinate systems to predict the fatigue lives of new material orientations. Biaxial low-cycle fatigue tests are conducted to verify the model. The prediction of the model agrees with the experimental results reasonably well. 相似文献
126.
An electroimpact compaction method recently developed for powder consolidation is described In terms of the basic principles of electric discharge and dynamic compaction processes. The influence of processing parameters, microstructural characteristics and mechanical properties of preforms obtained are discussed. Mathematical models for the mechanics of compaction, electrical resistance, discharge current variations and comparisons with experimental results are presented. The best set of properties are obtained when electrical discharge is applied to cause interparticle fusion at the instant when dynamic compaction pressure attains its peak level. 相似文献
127.
J. Hong E. S. Lambers C. R. Abernathy S. J. Pearton R. J. Shul W. S. Hobson 《Journal of Electronic Materials》1998,27(3):132-137
Dry etching of InGaP, AlInP, and AlGaP in inductively coupled plasmas (ICP) is reported as a function of plasma chemistry (BCl3 or Cl2, with additives of Ar, N2, or H2), source power, radio frequency chuck power, and pressure. Smooth anisotropic pattern transfer at peak etch rates of 1000–2000Å·min?1 is obtained at low DC self-biases (?100V dc) and pressures (2 mTorr). The etch mechanism is characterized by a trade-off between supplying sufficient active chloride species to the surface to produce a strong chemical enhancement of the etch rate, and the efficient removal of the chlorinated etch products before a thick selvedge layer is formed. Cl2 produces smooth surfaces over a wider range of conditions than does BCl3. 相似文献
128.
JA McCrohon WA Walters JT Robinson RJ McCredie L Turner MR Adams DJ Handelsman DS Celermajer 《Canadian Metallurgical Quarterly》1997,29(7):1432-1436
OBJECTIVES: We sought to assess whether high dose estrogen treatment is associated with enhanced arterial reactivity in genetic males. BACKGROUND: Although estrogens have been shown to enhance arterial reactivity in women, and are thereby thought to confer cardiovascular benefit, the vascular effects of long-term estrogen therapy in genetic males is unknown. METHODS: We studied the arterial physiology of 30 genetic males--15 male to female transsexuals receiving long-term high dose estrogen therapy and 15 healthy male control subjects matched for age, smoking history and vessel size. Using external vascular ultrasound, brachial artery diameter was measured at rest, after flow increase (causing endothelium-dependent dilation [EDD]) and after nitroglycerin (GTN), an endothelium-independent dilator. Blood pressure, cholesterol and testosterone levels were also measured in each subject. RESULTS: Total testosterone and free testosterone index levels were lower in the transsexuals compared with the control subjects (p < 0.001). In contrast, EDD was significantly higher in the transsexuals than in the control males (mean [+/-SD] 7.1 +/- 3.1% vs. 3.2 +/- 2.8%, p = 0.001), as was the GTN response (21.2 +/- 6.7% vs. 14.6 +/- 3.3%, p = 0.002). Total and high density lipoprotein cholesterol, blood pressure levels and baseline vessel size were similar in the two groups. On multivariate analysis, enhanced EDD was associated independently with estrogen therapy (p = 0.02) and with low total cholesterol (p = 0.04). An enhanced GTN response was also significantly associated with estrogen therapy (p = 0.03). CONCLUSIONS: Long-term treatment with high dose estrogens is associated with enhanced arterial reactivity in genetic males, which may be due to the effects of estrogen excess or androgen deprivation, or both. 相似文献
129.
Since its introduction into the analytical laboratory, CE has had to prove that it was capable of generating results comparable to HPLC or GC techniques in the six areas (specificity, precision, accuracy, linearity, ruggedness, and range) typically required of validated methods intended for submission to governmental agencies. This paper will showcase the development and validation of two analytical methods: one for specific identification of HEPES (N-[2-hydroxyethyl]piperazine-N'-[2-ethane sulfonic acid]) and the other to quantitate millimolar concentrations of tris (tris[hydroxymethyl]aminomethane) in high electrolyte solutions. Utilizing neutral markers and internal standards, results for HEPES demonstrate that migration time reproducibility, expressed as %RSD of 2% or less on a variety of capillaries, is obtainable. Additionally, for quantitation of tris, the values obtained for accuracy (%relative mean bias), precision (%RSD), and linearity (r2) over multiple days and capillaries meet the rigorous standards we require of HPLC or GC methods. 相似文献
130.
Hyperphosphorylated tau is the major component of paired helical filaments in neurofibrillary lesions associated with Alzheimer's disease. Hyperphosphorylation reduces the affinity of tau for microtubules and is thought to be a critical event in the pathogenesis of this disease. Recently, glycogen-synthase kinase-3 has been shown to phosphorylate tau in vitro and in non-neuronal cells transfected with tau. The activity of glycogen-synthase kinase-3 can be down-regulated in response to insulin or insulin-like growth factor-1 through the activation of the phosphatidylinositol 3-kinase pathway. We therefore hypothesize that insulin or insulin-like growth factor-1 may affect tau phosphorylation through the inhibition of glycogen-synthase kinase-3 in neurons. Using cultured human neuronal NT2N cells, we demonstrate that glycogen-synthase kinase-3 phosphorylates tau and reduces its affinity for microtubules and that insulin and insulin-like growth factor-1 stimulation reduces tau phosphorylation and promotes tau binding to microtubules. We further demonstrate that these effects of insulin and insulin-like growth factor-1 are mediated through the inhibition of glycogen-synthase kinase-3 via the phosphatidylinositol 3-kinase/protein kinase B signaling pathway. 相似文献