全文获取类型
收费全文 | 5555篇 |
免费 | 119篇 |
国内免费 | 13篇 |
专业分类
电工技术 | 37篇 |
综合类 | 3篇 |
化学工业 | 484篇 |
金属工艺 | 81篇 |
机械仪表 | 64篇 |
建筑科学 | 50篇 |
能源动力 | 68篇 |
轻工业 | 113篇 |
水利工程 | 1篇 |
石油天然气 | 4篇 |
无线电 | 400篇 |
一般工业技术 | 442篇 |
冶金工业 | 3586篇 |
原子能技术 | 28篇 |
自动化技术 | 326篇 |
出版年
2023年 | 7篇 |
2022年 | 20篇 |
2021年 | 21篇 |
2020年 | 26篇 |
2019年 | 25篇 |
2018年 | 48篇 |
2017年 | 47篇 |
2016年 | 47篇 |
2015年 | 50篇 |
2014年 | 71篇 |
2013年 | 183篇 |
2012年 | 103篇 |
2011年 | 131篇 |
2010年 | 118篇 |
2009年 | 120篇 |
2008年 | 128篇 |
2007年 | 111篇 |
2006年 | 77篇 |
2005年 | 71篇 |
2004年 | 63篇 |
2003年 | 79篇 |
2002年 | 50篇 |
2001年 | 49篇 |
2000年 | 56篇 |
1999年 | 195篇 |
1998年 | 1247篇 |
1997年 | 642篇 |
1996年 | 457篇 |
1995年 | 237篇 |
1994年 | 224篇 |
1993年 | 205篇 |
1992年 | 55篇 |
1991年 | 57篇 |
1990年 | 57篇 |
1989年 | 67篇 |
1988年 | 57篇 |
1987年 | 55篇 |
1986年 | 47篇 |
1985年 | 55篇 |
1984年 | 7篇 |
1983年 | 18篇 |
1982年 | 19篇 |
1981年 | 24篇 |
1980年 | 22篇 |
1978年 | 13篇 |
1977年 | 61篇 |
1976年 | 134篇 |
1975年 | 11篇 |
1974年 | 4篇 |
1972年 | 3篇 |
排序方式: 共有5687条查询结果,搜索用时 15 毫秒
11.
Three distinct stages of kink band formation and propagation exist in ductile matrix composites subjected to compressive loading. These stages are called incipient kinking, transient kinking and kink band broadening. Each stage involves a different deformation mode. The mechanics governing each stage are discussed. Incipient kinking, where the peak load is attained, and kink band broadening, where the load attains a steady-state, are important in structural design. Two design philosophies are presented. References to pertinent literature are made throughout. 相似文献
12.
The use of drugs for common pregnancy complications like premature labor, hypertensive diseases, and premature rupture of membranes with chorioamnionitis is reviewed. In addition, new publications on antiviral drugs in HIV-positive pregnant patients are also discussed. Among the drugs, suppressing premature labor side-effects of beta-mimetics are of growing concern. The effectiveness of other agents like magnesium, indomethacin, and sulindac are addressed. The various mechanisms explaining the beneficial effect of magnesium in pre-eclampsia are reviewed and new data on antihypertensives, such as labetalol, calcium channel blockers, and methyldopa are presented. The evidence from various clinical trials on the value of low-dose aspirin as a prophylactic agent against pregnancy-induced hypertension, pre-eclampsia, and intrauterine growth retardation in high-risk and low-risk patients is compared. Pharmacokinetic data including transplacental transfer of antibiotics and anti-HIV nucleosides are part of this review. 相似文献
13.
Follicular dendritic cell tumour of the liver is a recently recognized entity. To date, only two cases have been described, both in the pathology literature. Histologically, it resembles an inflammatory pseudotumour and immunohistochemical and ultrastructural studies are required for its diagnosis. The ultrasound, computed tomography and angiographic features of two cases of follicular dendritic cell tumour of the liver are described in detail. One of the patients had multiple recurrences of this tumour. The imaging features are very similar to those of hepatocellular carcinoma. As follicular dendritic cell tumour is considered to be of low-grade malignant potential, in contrast to the dismal prognosis for hepatocellular carcinoma, it is important to be able to accurately distinguish between the two types of tumour prior to initiating definitive therapy. 相似文献
14.
DE Anderson XJ Yuan CM Tseng LJ Rubin GM Rosen ML Tod 《Canadian Metallurgical Quarterly》1993,193(3):878-885
Free radicals react with nitrones to form stable nitroxides which can be identified by ESR spectroscopy. Unfortunately, little is known regarding the pharmacological properties of these compounds. In this study, three commonly used nitrones, 5,5-dimethylpyrroline-N-oxide (DMPO), alpha-phenyl-tert-butylnitrone (PBN), and alpha-(4-pyridyl 1-oxide)-N-tert-butylnitrone (POBN), were found to induce relaxation of preconstricted isolated rat pulmonary artery rings. Additional experiments with PBN indicated that vasorelaxation could not be attributed to production of endothelial derived factors, prostaglandins, or free radicals. Patch-clamp techniques revealed reversible calcium channel blockade with PBN at a concentration below that needed to detect free radicals. Calcium channel blockade probably accounts for the vasorelaxation observed in the isolated ring preparations described here, and should be considered when using nitrone spin-traps both in in vivo and clinical studies. 相似文献
15.
16.
17.
The interfacial stress intensity factors for three types of sandwich specimens: the single edge crack tensile specimen, the three point bend specimen and the four point shear specimen were obtained by the finite element analysis and compared with the asymptotic solutions. The results show that the geometric effect for mode II specimen is larger than mode I specimen. The limit curves for geometry factor equal to 1.05 were obtained to indicate the usable range of validity of the asymptotic solution. 相似文献
18.
A patient who developed a mixed neuroendocrine carcinoma and adenocarcinoma at the site of a previous long-standing ileostomy is reported. The neuroendocrine features are documented by both ultrastructural and immunocytochemical findings. Carcinoma arising in an ileostomy site is rare but has been recorded in patients with long-standing ileostomies after colectomy for chronic inflammatory bowel disease, as in this patient. Neuroendocrine carcinoma developing in this setting apparently has not been described before, however. 相似文献
19.
JP Grass IB Dockendorff VA Soto PH Araya CM Henriquez 《Canadian Metallurgical Quarterly》1993,18(3):336-338
A case report of a 10-year old girl with a herniated disc is presented. The most significant symptoms were progressive scoliosis with a flat back and paravertebral muscle spasm. An absent H reflex on the left and an increased latency of the somatosensory-evoked potentials of the left posterior tibial nerve were found. The computed tomographic scan of the lumbar spine showed a large central left-sided disc protrusion at the L5-S1 level. Our case presents the youngest patient with documented intervertebral disc herniation and the only one with severe scoliosis and vertebral rotation. The curve was not structural because it improved with surgery and an orthosis was not necessary. 相似文献
20.
An early step in the development of vertebrae, ribs, muscle, and dermis is the differentiation of the somitic mesoderm into dermomyotome dorsally and sclerotome ventrally. To analyze this process, we have developed an in vitro assay for somitic mesoderm differentiation. We show that sclerotomal markers can be induced by a diffusible factor secreted by notochord and floor plate and that heterologous cells expressing Sonic hedgehog (shh/vhh-1) mimic this effect. In contrast, expression of dermomyotomal markers can be caused by a contact-dependent signal from surface ectoderm and a diffusible signal from dorsal neural tube. Our results extend previous studies by suggesting that dorsoventral patterning of somites involves the coordinate action of multiple dorsalizing and ventralizing signals and that a diffusible form of Shh/Vhh-1 mediates sclerotome induction. 相似文献