首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   4962篇
  免费   4篇
电工技术   2篇
化学工业   71篇
金属工艺   2篇
建筑科学   1篇
矿业工程   2篇
能源动力   3篇
轻工业   7篇
石油天然气   3篇
无线电   19篇
一般工业技术   14篇
冶金工业   4831篇
自动化技术   11篇
  2021年   1篇
  2020年   2篇
  2019年   1篇
  2018年   7篇
  2017年   2篇
  2016年   1篇
  2015年   4篇
  2014年   1篇
  2013年   3篇
  2012年   1篇
  2011年   8篇
  2010年   8篇
  2009年   5篇
  2008年   7篇
  2007年   3篇
  2005年   5篇
  2004年   4篇
  2003年   18篇
  2002年   3篇
  2001年   5篇
  2000年   4篇
  1999年   151篇
  1998年   1463篇
  1997年   871篇
  1996年   542篇
  1995年   302篇
  1994年   271篇
  1993年   295篇
  1992年   31篇
  1991年   63篇
  1990年   58篇
  1989年   64篇
  1988年   62篇
  1987年   53篇
  1986年   63篇
  1985年   48篇
  1984年   1篇
  1983年   10篇
  1982年   22篇
  1981年   28篇
  1980年   26篇
  1979年   3篇
  1978年   13篇
  1977年   128篇
  1976年   286篇
  1975年   9篇
  1962年   1篇
  1955年   5篇
  1924年   2篇
  1920年   1篇
排序方式: 共有4966条查询结果,搜索用时 15 毫秒
41.
On curettage, done in a 39 year old patient because of metorrhagia, a peanut-sized nodule was scraped away from the endometrium. Histologically it consisted of a jumble of irregularly shaped portions of normal appearing embryonal cartilage, of tortuous thick-walled vessels, of twisted bundles of nerves of ducts of respiratory and intestinal epithelium, and of sheets of hornifying skin. The haphazard disarray of tissues supported the notion that the lesion was not a remnant of a malformed embryo. Step-sections through the lesion revealed no traces of placental villi or decidua in the surrounding endometrium. The following were considered as possible origins of the teratoma: 1. displaced germinal cells, 2. retention of pluripotent müllerian epithelium, 3. overaged or blighted ovum. The latter seems most compatible with the histological findings.  相似文献   
42.
43.
Two experiments were conducted to investigate the effects of varying levels of pantothenic acid on the efficiency of energy utilization and changes in body composition of the growing chick. The results indicate that a pantothenic acid deficiency does not interfere with the chick's ability to obtain metabolizable energy from the diet. The data do show that the efficiency of energy utilization and body composition were markedly affected when chicks were fed diets deficient in pantothenic acid. In both experiments, protein, fat and energy stores were significantly reduced when pantothenic acid-deficient diets were fed. Increased estimates of heat increment per gram of diet were observed when levels of pantothenic acid below the N.R.C. (1971) recommended level of 10 mg. per kg of diet were fed.  相似文献   
44.
Phase I studies were conducted in 58 adult cancer patients with Baker's Antifol (BAF), a new active-site directed inhibitor of dihydrofolate reductase. Dose escalation ranged from 10 to 250 mg/m2/day X 5 days and courses of treatment were repeated every 2-3 weeks. Biologic effects were observed mostly at doses greater than 100 mg/m2/day X 5 days. The patients developed myelosuppression during 19% of the trials. Other types of toxicity were dermatitis in 12 to 30% and stomatitis in 7 to 38% of the trials. Toxicity was directly related to the impairment of the patient's liver function. Two partial responses (in a patient with adenocarcinoma of the lung and a patient with transitional cell carcinoma of the bladder) occurred. BAF is an active new chemotherapeutic agent which deserves further clinical trials in patients with various malignancies.  相似文献   
45.
46.
BACKGROUND: To determine the effects of anatomic site on the presentation and diagnosis of malignant peripheral nerve sheath tumors (MPNSTs) and on the treatment and outcomes of the patients, the authors initiated a study of these tumors at different sites. An earlier report described MPNSTs of the buttock and lower extremity, and the current series analyzes those presenting at intrathoracic (IT) and subdiaphragmatic (SD) paraspinal sites. METHODS: The authors reviewed data on patients with paraspinal MPNSTs who were seen at Memorial Hospital during the period 1960-1995 and for whom histologic slides were available. Various clinicopathologic parameters and their effects on patient outcomes were examined. RESULTS: Twenty-five patients with 26 tumors were evaluated. Seven tumors were IT and 19 were SD; 60% of the patients had neurofibromatosis type 1 (NF1). Most patients presented with pain, and a diagnostic delay (of 3 months to 2 years) was often noted. Mean tumor sizes for SD and IT tumors were 14.3 cm and 6.6 cm, respectively. Most MPNSTs were composed of spindle cells in fascicles. Twenty-seven percent exhibited divergent differentiation. Twenty-four tumors were high grade, and a low grade component was identified in 8 tumors. Surgical resection was attempted for 23 tumors (88%), but complete resection was achieved in only 6 cases (23%). Eighty percent of the patients died of their tumors, 2-year and 5-year survival rates were 35% and 16%, and median survival was 8.5 months. Significant prognostic factors were tumor size <5 cm, the presence of a low grade component, and complete tumor resection. CONCLUSIONS: Paraspinal MPNSTs have more aggressive behavior than peripherally located tumors, mainly because of the difficulty encountered in resecting them completely. Prognoses of patients with MPNST at this site appear to be affected by resection status, tumor size, and tumor grade.  相似文献   
47.
We calculated the electrostatic force between a planar interface, such as a planar-supported lipid bilayer membrane, and the tip of a stylus on which another lipid bilayer or some other biomacromolecular system might be deposited. We considered styli with rounded tips as well as conical tips. To take into account the effect of dynamical hydrogen-bonded structures in the aqueous phase, we used a theory of nonlocal electrostatics. We used the Derjaguin approximation and identified the systems for which its use is valid. We pointed out where our approach differs from previous calculations and to what extent the latter are inadequate. We found that 1) the nonlocal interactions have significant effects over distances of 10-15 A from the polar zone and that, at the surface of this zone, the effect on the calculated force can be some orders of magnitude; 2) the lipid dipoles and charges are located a distance L from the hydrophobic layer in the aqueous medium and this can have consequences that may not be appreciated if it is ignored; 3) dipoles, located in the aqueous region, can give rise to forces even though the polar layer is unchanged, and if this is ignored the interpretation of force data can be erroneous if an attempt is made to rationalize an observed force with a knowledge of an uncharged surface; 4) the shape of the stylus tip can be very important, and a failure to take this into account can result in incorrect conclusions, a point made by other workers; and 5) when L is nonzero, the presence of charges and dipoles can yield a force that can be nonmonotonic as a function of ionic concentration.  相似文献   
48.
This study was designed to evaluate the effect of laser energy at nonablative levels on the ultrastructure of joint capsular collagen. The femoropatellar joint capsules of six mature New Zealand white rabbits were harvested immediately after death. Specimens were divided into three treatment groups (5, 10, and 15 watts) and one control group. Laser energy was applied using a holmium: YAG laser. Transmission electron microscopy showed significant ultrastructural alterations in collagenous architecture for all laser treatment groups, with increased fibril cross-sectional diameter for each of the treated groups. The fibrils began to lose their distinct edges and their periodical cross-striations at subsequently higher energy densities. A morphometric analysis showed that each subsequently higher laser energy caused a significant increase in collagen fibril diameter. Ultrastructural alteration of collagen fibril architecture caused by the thermal effect of laser energy is probably the dominant mechanism of laser-induced tissue shrinkage.  相似文献   
49.
Eighteen and 23 FAA components were detected in the cyst wall and cyst fluid of E granulosus, respectively, by using automatic amino acid analyzer. The concentrations of most of the determined FAA were higher in the cyst fluid than those in the cyst wall, especially the taurine was 5-fold higher. Mebendazole treatment resulted in an increase in the concentration of alanine, valine, lysine, and taurine in both cyst wall and cyst fluid, the most notable being the alanine in the cyst wall. The results are interpreted as a coupling of glycolysis and amino acid metabolism, suggesting an involvement of FAA metabolism in the mechanism of Meb action.  相似文献   
50.
This study introduces the conception of an apparatus to crystallize continuously nanosized explosive or more generally nanosized organic materials. These materials can be elaborated in pure state or in form of mixtures of energetic and inert materials. The installation can produce nano‐RDX or nano‐PETN from 1 to 10 g h−1 using a reactor containing one ultrasonic piezoelectric transducer. The present study describes the different parameters which influence the crystallization process. It presents first results of the parametric study of the influence of these parameters. The most important parameters which were already identified are the frequency of the ultrasonic piezoelectric transducer, the nature of the solvent, the liquid level in the reactor, the temperatures in the system, and the passing time of the aerosol droplets in the oven.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号