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   2088篇
  免费   3篇
化学工业   18篇
金属工艺   2篇
机械仪表   3篇
建筑科学   5篇
轻工业   4篇
石油天然气   1篇
无线电   3篇
一般工业技术   13篇
冶金工业   2040篇
原子能技术   2篇
  2022年   1篇
  2020年   3篇
  2019年   1篇
  2018年   1篇
  2017年   1篇
  2015年   1篇
  2014年   1篇
  2013年   1篇
  2012年   2篇
  2011年   5篇
  2010年   1篇
  2008年   2篇
  2007年   1篇
  2006年   1篇
  2004年   2篇
  2003年   8篇
  2002年   2篇
  2000年   1篇
  1999年   57篇
  1998年   626篇
  1997年   365篇
  1996年   218篇
  1995年   151篇
  1994年   108篇
  1993年   134篇
  1992年   22篇
  1991年   34篇
  1990年   29篇
  1989年   31篇
  1988年   27篇
  1987年   23篇
  1986年   24篇
  1985年   24篇
  1984年   1篇
  1983年   2篇
  1982年   9篇
  1981年   14篇
  1980年   20篇
  1978年   4篇
  1977年   45篇
  1976年   83篇
  1975年   2篇
  1974年   1篇
  1970年   1篇
  1968年   1篇
排序方式: 共有2091条查询结果,搜索用时 15 毫秒
991.
992.
BACKGROUND: Empirical definitions of remission and recovery from eating disorders are needed to understand outcome data and compare results across studies. METHOD: 106 treatment-seeking women with bulimia nervosa, who had abstained from binging and purging for at least 4 weeks, were followed prospectively. Relapse was defined as at least 4 consecutive weeks of either binging and purging weekly or binging two or more times per week, regardless of purging. Recovery was differentiated from remission based on the probability of relapse. The minimum number of weeks after which the risk of relapse leveled off was used as the cut-off to distinguish between the two outcomes. Kaplan-Meier methods were used to estimate the weekly probability of relapse. RESULTS: When defining remission as at least 4 weeks of being asymptomatic, a quarter of the women relapsed within 11 weeks. By 37 weeks, only 49% of the women remained asymptomatic (95% CI, 41-61). The probability of relapse was substantial for approximately a year after a woman ceased to binge and purge. CONCLUSION: Bulimia nervosa is an episodic disorder. As a conservative approach, periods of being asymptomatic that last less than 1 year should be labeled as remissions, not recoveries.  相似文献   
993.
Immature dendritic cells (DC) use both macropinocytosis and mannose receptor-mediated endocytosis to internalize soluble Ags efficiently. These Ags are ultimately presented to T cells after DC maturation and migration into the lymph nodes. We have previously described the immortalized myeloid cell line FSDC as displaying the characteristics of early DC precursors that efficiently internalize soluble Ags. To describe the different routes of Ag uptake and to identify the Ag retention compartments in FSDC, we followed the intracellular fate of FITC-coupled OVA, dextran (DX), transferrin, and Lucifer Yellow using flow cytometry, confocal microscopy, and immunoelectron microscopy. OVA and DX gained access into macropinosomes and early endosomes. DX was preferentially sorted into endosomal compartments, while most of the OVA entered macropinosomes via fluid phase uptake. We found a long-lasting retention of DX and OVA of up to 24 h. After 6 h of chase, these two molecules were concentrated in common vesicular compartments. These retention compartments were distinct from endosomes and lysosomes; they were much larger, only mildly acidic, and lacked the small GTP binding protein rab7. However, they were positive for lysosome-associated membrane protein-1, the protease cathepsin D, and MHC class II molecules, thus representing matured macropinosomes. These data suggest that the activity of vacuolar proteases is reduced at the mildly acidic pH of these vesicles, which explains their specific retention of an Ag. The retention compartments might be used by nonlymphoid tissue DC to store peripheral Ags during their migration to the lymph node.  相似文献   
994.
995.
Amyloid deposition is associated with a diverse range of disorders that includes Alzheimer's disease, type II diabetes mellitus and dialysis arthropathy. Although less common, systemic AA and AL amyloidosis remain important because effective treatments have increasingly become available. The pathology in all forms of amyloidosis involves the extracellular deposition of protein as characteristic fibrillar aggregates which interfere with tissue structure and function. Amyloid fibrils are derived from different unrelated proteins in the different forms of the disease but share many common properties, including the capacity to bind the normal plasma protein serum amyloid P component (SAP). This is the basis for our development of radiolabelled SAP as a nuclear medicine tracer for the diagnosis and quantitative monitoring of amyloid. Serial studies have shown that the deposits are far from inert but are actually turned over quite rapidly in many patients. The treatment of amyloidosis involves supportive measures whilst every effort is made to reduce the supply of the respective fibril precursor protein. Under favourable circumstances further amyloid deposition will be prevented. existing deposits will regress and improvement of organ function will occur. Since this strategy is not always possible or may fail, new approaches to inhibit fibril formation and promote regression of amyloid are being pursued.  相似文献   
996.
Ethnic identity and conflict in Guatemala, Peru, and Puerto Rico are complexly embedded within dynamic systems of class- and race-based geopolitics. Whereas overt violence and terror have permeated both Guatemalan and Peruvian societies, overt conflict has undermined Puerto Rican nationhood. Despite similarities among these 3 countries of Hispano-America, there are important particularities that inform psychological theory and practice. This article explores selected contributions of a psychology of liberation informed by indigenous psychologies and reflexive praxis. The challenges these conflicts and their consequences pose to psychologists seeking to work with populations most deeply affected by these social inequalities are analyzed. It concludes with suggestions of how psychology can move toward the development of community-based responses to psychosocial oppression that foster enhanced individual and collective development in a context of social change.  相似文献   
997.
BACKGROUND: To determine the relationship between DNA polymorphisms in the angiotensin I converting enzyme (ACE) gene, serum ACE activity and the risk of diabetic nephropathy. METHODS: A case-control study was carried out in a population of Jewish insulin-dependent diabetes mellitus (IDDM) patients. Cases (77 IDDM patients with diabetic nephropathy) and controls (89 IDDM patients with normoalbuminuria) were genotyped with PCR protocols for detecting two DNA polymorphisms in the ACE gene: one in intron 7 detected with the restriction enzyme PstI and the other in intron 16 identified as an insertion/deletion (I/D). RESULTS: The risk of nephropathy was increased only in patients homozygous for the allele with the PstI site. These homozygotes had a nephropathy risk that was 2.3 times (95% C.I.: 1.2-4.5) that of the other genotypes. Furthermore, these individuals did not have elevated serum ACE activity. CONCLUSIONS: The results of this study are evidence that the risk of diabetic nephropathy in IDDM is influenced by genetic variability at the ACE locus, but the responsible variant is not the I/D polymorphism in intron 16. Our findings require further studies in other populations.  相似文献   
998.
An expert workshop reviewed the health effects of n-3 polyunsaturated fatty acids (PUFA), and came to the following conclusions. 1. Consumption of fish may reduce the risk of coronary heart disease (CHD). People at risk for CHD are therefore advised to eat fish once a week. The n-3 PUFA in fish are probably the active agents. People who do not eat fish should consider obtaining 200 mg of very long chain n-3 PUFA daily from other sources. 2. Marine n-3 PUFA somewhat alleviate the symptoms of rheumatoid arthritis. 3. There is incomplete but growing evidence that consumption of the plant n-3 PUFA, alpha-linolenic acid, reduces the risk of CHD. An intake of 2 g/d or 1% of energy of alpha-linolenic acid appears prudent. 4. The ratio of total n-3 over n-6 PUFA (linoleic acid) is not useful for characterising foods or diets because plant and marine n-3 PUFA show different effects, and because a decrease in n-6 PUFA intake does not produce the same effects as an increase in n-3 PUFA intake. Separate recommendations for alpha-linolenic acid, marine n-3 PUFA and linoleic acid are preferred.  相似文献   
999.
BACKGROUND: Primary liver cancer is an important health problem in Korea, where hepatitis B virus (HBV) infection is prevalent. The authors conducted a prospective cohort study to evaluate the protective effect of HBV vaccination against liver cancer in adults. METHODS: A total of 370,285 males aged > or = 30 comprised the study population. They were clinically free of liver diseases, and had not been vaccinated against HBV at enrolment. The results of HBV surface antigen (HBsAg) and antibody to HBsAg (anti-HBs) marker positivity and those of the vaccination programme which took place during 1985 were used for the construction of the cohort. About 5% (n = 18,914) were HBsAg positive, 78,094 were anti-HBs positive, and 273,277 were negative for both. Among the candidates for HBV vaccination (n = 273,277), 35,934 (13.2%) people had been vaccinated against HBV during 1985. Cases of liver cancer were ascertained by record linkage and from medical records covering 1986-1989. A multivariate log-linear model was used to test statistical significance and to estimate relative risks (RR). RESULTS: The total follow-up period was 1,404,566 person-years, with an average of 3 years and 10 months. A total of 302 incident cases were ascertained. The overall incidence rate of liver cancer was 21.7 per 100,000 person-years. With reference to the incidence level among the unvaccinated and uninfected, the RR of primary liver cancer among the chronically infected and that of the unvaccinated and infected was 18.1 (95% CI: 14.2-22.9) and 0.34 (95% CI: 0.19-0.60), respectively. The RR among the vaccinated group was 0.58 (95% CI: 0.31-1.09). CONCLUSIONS: This study suggested that artificial immunization through HBV vaccination, even in adulthood, reduces the risk of liver cancer. It might also offer a practicable means of primary prevention, especially in areas with hyperendemicity of HBV infection.  相似文献   
1000.
Mice bearing a disrupted C3 locus (C3-/-) have an impaired Ab response to T-dependent Ags (bacteriophage phiX 174 and nuclear protein-keyhole limpet hemocyanin) characterized by a reduction in number and size of germinal centers and impaired retention of Ag by follicular dendritic cells. To test the importance of C3 synthesized locally within the lymphoid compartment during an immune response to T-dependent Ag, we reconstituted C3-/- mice with wild-type bone marrow of MHC-identical littermates. Engraftment not only restored local C3 synthesis in the spleen, but also rescued the impaired humoral response. The major source of C3 mRNA was MOMA-2+ macrophages localized within the white pulp areas of the spleen. Interestingly, C3 expression is apparently regulated as C3 mRNA was not detected in splenic sections of nonimmune mice. Furthermore, local C3 synthesis by donor macrophages reversed the impaired Ag trapping by splenic follicular dendritic cells in C3-deficient mice.  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