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   4702篇
  免费   10篇
电工技术   3篇
化学工业   56篇
金属工艺   24篇
机械仪表   8篇
建筑科学   18篇
能源动力   10篇
轻工业   75篇
水利工程   4篇
无线电   44篇
一般工业技术   63篇
冶金工业   4366篇
原子能技术   2篇
自动化技术   39篇
  2020年   3篇
  2019年   2篇
  2018年   3篇
  2017年   5篇
  2016年   7篇
  2015年   3篇
  2014年   5篇
  2013年   17篇
  2012年   8篇
  2011年   15篇
  2010年   12篇
  2009年   16篇
  2008年   29篇
  2007年   20篇
  2006年   13篇
  2005年   18篇
  2004年   20篇
  2003年   17篇
  2002年   18篇
  2001年   14篇
  2000年   6篇
  1999年   143篇
  1998年   1442篇
  1997年   803篇
  1996年   526篇
  1995年   269篇
  1994年   238篇
  1993年   262篇
  1992年   36篇
  1991年   45篇
  1990年   40篇
  1989年   53篇
  1988年   59篇
  1987年   30篇
  1986年   34篇
  1985年   35篇
  1984年   10篇
  1983年   12篇
  1982年   17篇
  1981年   20篇
  1980年   51篇
  1979年   7篇
  1978年   6篇
  1977年   92篇
  1976年   196篇
  1975年   12篇
  1974年   5篇
  1973年   6篇
  1972年   2篇
  1970年   6篇
排序方式: 共有4712条查询结果,搜索用时 15 毫秒
961.
Objective: To examine prospectively the relationships among psychological factors, rehabilitation adherence, and short-term rehabilitation outcome after knee surgery. Study Design and Participants: Individuals with acute anterior cruciate ligament (ACL) tears (N?=?95) completed measures of self-motivation, social support, athletic identity, and psychological distress before reconstructive surgery. After surgery, 93 participants reported on their completion of home rehabilitation exercises and cryotherapy, and their rehabilitation practitioners indicated the patients' attendance at, and adherence during, rehabilitation sessions. Rehabilitation outcome measures were taken from 69 participants approximately 6 months postsurgery. Main Outcome Measures: Knee laxity, functional ability, and subjective symptoms were the primary outcomes assessed. Results: Self-motivation was significant predictor of home exercise completion; athletic identity and psychological distress were significant predictors of knee laxity; and attendance at rehabilitation sessions and home cryotherapy completion were significant predictors of functional ability. Rehabilitation adherence did not mediate the relationship between psychological factors and rehabilitation outcome. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
962.
The role of dissolved oxygen, and of active species generated by photo-induced reactions with oxygen, in the photocatalytic degradation of phenol was investigated using polymer [poly-(fluorene-co-thiophene) with thiophene content of 30%, so-called PFT30] sensitized TiO2 (PFT30/TiO2) under visible light irradiation. The photoluminescent (PL) quantum yield of PFT30/TiO2 was about 30% of that of PFT30/Al(2)O(3), proving that electron transfer took place between the polymer and TiO2. The result that photocatalytic degradation of phenol was almost stopped when the solution was saturated with N(2) proved the importance of O(2). Addition of NaN(3), an effective quencher of singlet oxygen ((1)O(2)), caused about a 40% decrease in the phenol degradation ratio. Addition of alcohols caused about a 60% decrease in the phenol photodegradation ratio, indicating that the hydroxyl radicals (OH), whose presence was confirmed by electron spin resonance (ESR) spectroscopy, was the predominant active species in aqueous solution. In anhydrous solution, singlet oxygen ((1)O(2)) was the predominant species. These results indicate that oxygen plays a very important role in the photocatalytic degradation of phenol.  相似文献   
963.
964.
ABSTRACT:  Beef complexus (chuck), serratus ventralis (chuck), vastus lateralis (round), vatsus medialis (round), and longissimus dorsi (loin) muscles were enhanced (0.3% salt, 0.4% phosphate), vacuum packaged, and aged for 7 or 14 d. Enhancement increased positive sensory attributes (tenderness, juiciness, beef flavor, saltiness) and decreased negative attributes (off-flavors) of all muscles but had greater effects on some than on others. It increased the oily mouthfeel (10%) and saltiness (40%) and decreased the L * value and chroma of the complexus (chuck). It increased tenderness, juiciness, and beef flavor and decreased off-flavors, visual red and brown colors, shear value, and cook loss of the serratus ventrali (chuck) , vastus lateralis (round), vastus medialis (round), and longissiumus dorsi (loin). Aging slightly decreased rancid and liver off-flavor scores, visual brown color, and shear value and increased the hue angle and L * and b * values.  相似文献   
965.
We describe a 31-year-old man who developed sudden painful loss of vision in the right eye and was found to have a retrobulbar optic neuropathy. Magnetic resonance (MR) imaging gave normal results, and a diagnosis of retrobulbar optic neuritis was made. The patient was treated with oral prednisone, but he continued to lose vision in the right eye and then began to lose vision in the left eye. Repeat MR imaging performed eight weeks after the initial study showed a giant intracranial aneurysm compressing the right and left optic nerves. Cerebral angiography revealed that the aneurysm arose from the origin of the right ophthalmic artery. Treatment of the aneurysm by a trapping procedure resulted in improvement in vision in the left eye but no change in vision in the right eye. This report emphasizes the difficulty in imaging intracranial aneurysms of various sizes, the rapidity with which intracranial aneurysms can enlarge, and the importance of continued follow-up examinations in patients thought to have idiopathic optic neuritis.  相似文献   
966.
OBJECTIVE: A mutant soybean line (A16) low in linolenic acid content (2% of oil by weight) was developed to increase oil oxidative stability. It was unknown whether serum lipid and lipoprotein concentrations in humans would be affected should A16 soybean oil (A16 oil) replace commercial soybean oil in diets. This study was conducted to examine the hypothesis that in free-living normolipidemic women, the consumption of A16 oil at approximately 10% of energy intake (en%) would not affect serum lipids and lipoproteins differently than would the consumption of the same amount of a commercial soybean oil with 7% of linolenic acid content. DESIGN: Fifteen free-living female college students consumed the soybean oil daily with regular meals for 9 weeks in different orders, with each test oil being eaten for 3 weeks. During the study, 13 en% was provided by each test oil and a total of 35 en% was from dietary fat. Serum concentrations of total cholesterol, high-density lipoprotein cholesterol (HDL cholesterol), low-density lipoprotein cholesterol (LDL cholesterol) and triacylglycerides (TAG) were measured. Serum total fatty acid patterns were analyzed as well. RESULTS: Each of the three test oils decreased serum total cholesterol, LDL cholesterol and TAG concentrations from the baseline values. The feeding of A16 and commercial soybean oils decreased serum HDL cholesterol significantly compared with coconut oil (p < 0.05). Dietary inclusion of coconut oil increased serum myristic acid significantly more than did either soybean oil (p < 0.01). Serum arachidonic acid concentrations were significantly greater with A16 consumption than with commercial soybean oil consumption (p < 0.001). CONCLUSION: A16 and commercial soybean oils both diminished serum HDL cholesterol. Although the fatty acid composition differed between the two soybean oils, A16 oil and commercial oil had similar effects on serum concentrations of lipoproteins and lipids. With increased oxidative stability, A16 oil is a good alternative to commercial soybean oil.  相似文献   
967.
Some chemotherapeutic agents, as well as TNF and Fas, induce apoptotic cell death in tumor cells, but the cellular components involved in the process have not yet been identified. Interleukin 1 beta converting enzyme (ICE) is a mammalian homolog of CED-3, a protein required for programmed cell death in nematode Caenorhabditis elegans. We found that a selective inhibitor of ICE/ced 3 family proteases, benzyloxycarbonyl Asp CH2OC(O) 2 6,-dichlorobenzene (Z-Asp-CH2-DCB). completely blocked the apoptotic cell death of human leukemia cells caused by etoposide, camptothecin, 1-beta-D-arabinofuranosyl cytosine (Ara-C) and adriamycin. Moreover, in antitumor agent-treated U937 cells, an ICE-like (CPP32-like) protease was strongly activated. These results indicate that ICE/ ced 3 family proteases are involved in antitumor agent-induced apoptosis. Activation of ICE family proteases plays a key role in apoptosis. However, the subsequent mechanisms resulting in apoptosis are largely unknown. We identified actin as a substrate of ICE family proteases. Cleavage of actin and other substrate proteins by ICE family proteases could be critical in the ongoing process of antitumor agent-induced apoptosis in tumor cells.  相似文献   
968.
Crystallite regions within a hydrogel network contribute to its mechanical strength, which is crucial for use in load-bearing applications. However, high amounts of crystallinity can negatively impact the ability for hydrogels to be injected, an attractive property that could replace the need for highly invasive surgical procedures. The reversibility of crystallinity and its lasting impact on the injectability of poly(vinyl alcohol) and poly(ethylene glycol) hydrogels was evaluated in this paper. The relative percent crystallinity in hydrogels was evaluated after storage and autoclaving in syringes in weekly intervals using X-ray diffraction. Results indicate that crystallinity increased over time and significantly decreased after autoclaving for all samples, where postautoclaved samples contained comparable crystallinity percentages to freshly made gels (p > 0.05). Injectability was evaluated using calculated viscosity. Aged samples were able to be injected after autoclaving, yet there was no determination established between viscosity and storage times based on the data. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48706.  相似文献   
969.
Epidemiological aspects of bovine viral diarrhoea virus (BVDV) infections were studied longitudinally in a large dairy herd for three years. At the start of the study, practically all the cows more than four years old had BVDV antibody titres, whereas the younger stock were almost all seronegative. The spread of the virus was monitored in a part of the population that contained only transiently viraemic cattle and in another part that contained persistently viraemic calves. Among the lactating cows the virus circulated for two-and-a-half years, although they had no direct contact with persistently viraemic cattle during this period. The highest transmission rate occurred when a large number of susceptible heifers was added to the population of cows that contained transiently viraemic cattle. The circulation of BVDV among the lactating cows ceased while 27 seronegative cows were still present. Both findings are in accordance with predictions from simple epidemic models. The susceptibility of the cows that remained seronegative was confirmed experimentally. In contrast with the limited circulation of BVDV caused by transiently viraemic cattle, virtually all susceptible cattle that came into contact with a persistently viraemic calf became seropositive within three months. Transplacental BVDV infections were not detected in the calves born to cows that had antibodies against the virus due to an infection that had occurred at least four years earlier. Transplacental transmission of BVDV did not occur in most of the pregnant cows that were infected before approximately the 60th day of gestation, but when cows became infected later in gestation the virus virtually always invaded the fetus.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   
970.
OBJECTIVE: Our purpose was to evaluate our experience with estrogen replacement in women with a history of early-stage endometrial cancer and to determine whether it increased the risk for recurrence or death. STUDY DESIGN: A retrospective review was performed of 123 women with surgical stage I and II endometrial adenocarcinoma treated between 1984 and 1994; 62 had received estrogen replacement therapy after cancer therapy. Sixty-one women received no estrogen. Variables analyzed included age parity, surgical stage, grade, depth of myometrial invasion, presence of intercurrent illnesses, duration of follow-up, and duration of estrogen replacement, if applicable. Outcome variables assessed included recurrence rate, time to recurrence, and disease-free interval. RESULTS: The estrogen replacement therapy group had earlier stage disease (p = 0.04) and less severe depth of invasion (p = 0.003); however, the total number of deaths in each group was not significantly different. The disease-free survival in the estrogen replacement therapy group did not differ significantly compared with those not receiving estrogen replacement therapy. The data are suggestive of improved disease-free survival in the estrogen replacement therapy group, which may be related to differences in age, stage, grade, and depth of invasion. The overall recurrence rate was 6.5%, with an overall death rate of 1.6%. CONCLUSIONS: There is no evidence to suggest that estrogen decreased the disease-free interval or increased the risk for recurrence in early-stage disease.  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