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   3945篇
  免费   18篇
  国内免费   1篇
电工技术   15篇
综合类   2篇
化学工业   84篇
金属工艺   10篇
机械仪表   14篇
建筑科学   23篇
矿业工程   1篇
能源动力   4篇
轻工业   74篇
水利工程   4篇
石油天然气   1篇
无线电   62篇
一般工业技术   86篇
冶金工业   3526篇
原子能技术   5篇
自动化技术   53篇
  2021年   8篇
  2020年   8篇
  2019年   9篇
  2018年   4篇
  2017年   10篇
  2016年   13篇
  2015年   10篇
  2014年   9篇
  2013年   5篇
  2012年   18篇
  2011年   17篇
  2010年   19篇
  2009年   16篇
  2008年   23篇
  2007年   32篇
  2006年   20篇
  2005年   29篇
  2004年   12篇
  2003年   22篇
  2002年   8篇
  2001年   17篇
  2000年   10篇
  1999年   142篇
  1998年   1183篇
  1997年   615篇
  1996年   434篇
  1995年   214篇
  1994年   201篇
  1993年   183篇
  1992年   46篇
  1991年   42篇
  1990年   53篇
  1989年   52篇
  1988年   40篇
  1987年   40篇
  1986年   35篇
  1985年   49篇
  1984年   5篇
  1983年   7篇
  1982年   15篇
  1981年   15篇
  1980年   19篇
  1978年   9篇
  1977年   56篇
  1976年   141篇
  1975年   5篇
  1972年   3篇
  1970年   6篇
  1966年   3篇
  1934年   3篇
排序方式: 共有3964条查询结果,搜索用时 15 毫秒
991.
992.
OBJECTIVES: The purpose of the study was to describe the involvement of registered dietitians in parenteral nutrition (PN) orders, to identify characteristics of those who write orders; and to rank education, training, and support elements that dietitians believe facilitate PN order-writing skills. DESIGN: Mail survey method. SUBJECTS: Usable returned questionnaires (n = 266) represented randomly sampled membership of the Dietitians in Nutrition Support (a dietetic practice group of The American Dietetic Association) and registered dietitian membership of the American Society of Parenteral and Enteral Nutrition. STATISTICAL ANALYSIS: Data were analyzed using basic frequency displays on all questionnaire items, Pearson correlations between the quantitative variables, and one-way analysis of variance with each of the categorical variables and the quantitative variables. Detail exploration among variables was done by chi(2) analyses and two-tailed t tests. RESULTS: "Recommend" was the most frequent response to a query about participation in PN orders. An average of 37% of respondents sometimes or always wrote orders for nutrients. Specialists were more likely to write orders than clinicians and managers. No relationship was found between those who wrote orders and educational level, and writers had been registered for a shorter length of time. Agreement on the training and support needed for order-writing skills was nearly unanimous. APPLICATIONS: The PN skills of respondents who were specialists distinguished them from managers and clinicians. Specialists did not fit criteria for advanced practice, and specialty practice in metabolic nutrition care may be too broad to define their practice. Educators must recognize the importance of including PN training in didactic and clinical training programs. Registered dietitians with PN skills will be well positioned to play an active role in the evolving health care system.  相似文献   
993.
The complement phenotypes of Moraxella catarrhalis isolates obtained from adult patients with acute laryngitis were investigated using a microliter serum bactericidal assay and compared with those of other donor groups. Laryngitis isolates had a higher proportion (57%) of complement-resistant strains than did carrier strains from healthy 8- to 13-year-old schoolchildren (16%). The difference between these groups was statistically significant (chi2 [3 x 2 table] = 21.55; P < .001). The relatively frequent occurrence of the complement-resistant (virulence-associated) phenotype in adults with acute laryngitis supports the theory of an active role of M. catarrhalis in the pathogenesis of acute laryngitis.  相似文献   
994.
995.
The site of Klasies River Mouth (KRM) in South Africa has produced a small sample of early Upper Pleistocene hominid remains that have been a focus for discussions of the origins of modern humans. Despite certain primitive characteristics exhibited by these fossils, proponents of a single recent origin have attributed them to early modern humans. Critics of this hypothesis have emphasized the significance of the archaic features evident in this sample, including the absence of pronounced chins among the mandibular specimens. This study compares the size range and chin morphology exhibited by the KRM mandibles with that of Neandertals, Upper Pleistocene humans, and recent humans. The extreme sexual dimorphism documented among the KRM fossils reflects the presence of a very small individual, and previous efforts to classify the KRM sample as archaic on the basis of their robusticity have failed to address the significance of this diminutive hominid. While each KRM fossil falls within the 95% envelope of variability established for chin development in a comparative modern sample, a similarly low frequency of pronounced chins is very unlikely to be found in any recent human population. The morphological pattern of the KRM mandibles is clearly distinct from that of Neandertals and of recent humans.  相似文献   
996.
OBJECTIVE: To identify the origin of eosinophils in cases of eosinophil-associated preterm delivery. METHODS: From an established set of 465 consecutive non-anomalous singleton infants delivered at 22-32 weeks' gestation, we retrieved 161 cases of preterm delivery following spontaneous onset of preterm labor, 78 cases with maternal preeclampsia, 33 cases of abruption, and 193 cases of premature rupture of membranes (PROM). Charts were reviewed, and the placenta, umbilical cord, and membranes were examined histologically. In cases with extravascular eosinophils showing evident gradient toward the amniotic cavity, the origin of the eosinophils (fetal or maternal) was determined by the proximity to fetal or maternal vessels. RESULTS: Histologic evidence of an eosinophilic gradient toward the amniotic cavity was present only in the fetal (including umbilical cord and chorion) compartments. This eosinophilic gradient was present in 19% (90 of 465) of preterm delivery cases and was significantly more common in cases of PROM (54 of 193, 28%) and preterm labor (34 of 161, 21%) than abruption (two of 33, 6%) and preeclampsia (none of 78) (P < .001). In 84 of 90 cases (93%), the eosinophilic gradient was present along with multiple histologic indicators of acute intrauterine inflammation. CONCLUSION: An eosinophilic gradient toward the amniotic cavity, present in nearly a fifth of cases of preterm delivery, is probably of fetal origin, making it unlikely that a maternal "allergy-like" mechanism is a cause of preterm delivery.  相似文献   
997.
998.
BACKGROUND AND OBJECTIVES: Little is known about resolution of serum and cerebrospinal fluid abnormalities after neurosyphilis treatment, especially in patients infected with human immunodeficiency virus (HIV). GOAL: To examine the time course of resolution of these abnormalities. STUDY DESIGN: Case series of 22 patients with neurosyphilis (13 infected with HIV) with reactive cerebrospinal fluid Venereal Disease Research Laboratory test who underwent at least one lumbar puncture after treatment. RESULTS: Resolution of all serum and cerebrospinal fluid measures was slower in patients infected with HIV. Serum and cerebrospinal fluid abnormalities resolved in most patients not infected with HIV by 30 weeks, and all met Centers for Disease Control and Prevention criteria for cure. One patient infected with HIV failed therapy by Centers for Disease Control and Prevention criteria, and three others had persistent pleocytosis. CONCLUSIONS: HIV-infected patients with neurosyphilis have slower resolution of serum and cerebrospinal fluid abnormalities after therapy. This observation may suggest impaired clearance of Treponema pallidum from the central nervous system.  相似文献   
999.
The corneal wound-healing properties of fibronectin (FN) and a fibronectin hydrolysate (FNH) have been evaluated in comparison with commonly used drugs. Nonpenetrating bilateral surgical keratectomy was performed in male albino rabbits. The left eye was treated with the active product, whereas the right eye served as a control (vehicle). The healing area was measured by planimetry after fluorescein staining at 0, 24, 48, and 72 h after keratectomy. Histological and immunohistochemical analysis of the healing process was also performed. Results were as follows: (a) Nandrolone (p < 0.005) and asiaticoside (p < 0.001), both at 10 mg/ml, in eyedrops delayed the healing process. (b) An ointment containing vitamin A and amino acids also delayed the process but at the limit of statistical significance (p = 0.055). (c) FNH (20-80 mg prot/ml) significantly improved the quality and shortened the time of the healing process at 60 mg prot/ml and above. (d) Human FN (100-800 micrograms/ml) did not affect the healing process. Immunohistochemical analysis demonstrated that FNH accelerated the appearance of endogenous FN in the damaged cornea earlier than in the control eyes. It is concluded that FNH may be useful in the management of corneal wounds, whereas the effectiveness of FN is doubtful.  相似文献   
1000.
Intercellular communication is mediated by specialized cell-cell contact areas known as gap junctions. Connexins are the constitutive proteins of gap junction intercellular channels. Various cell expression systems are used to express connexins and, in turn, these expression systems can then be tested for their ability to form functional cell-cell channels. In this review, expression of murine endogenous connexins in primary cells and established cell lines is compared with results obtained by expression of exogenous connexins in Xenopus oocytes and cultured mammalian cells. In addition, first reports on characterization of connexin-deficient mice are discussed.  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