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   76841篇
  免费   3616篇
  国内免费   1525篇
电工技术   2333篇
技术理论   2篇
综合类   2857篇
化学工业   10578篇
金属工艺   2624篇
机械仪表   2872篇
建筑科学   3405篇
矿业工程   1459篇
能源动力   1268篇
轻工业   3944篇
水利工程   1123篇
石油天然气   2599篇
武器工业   244篇
无线电   5824篇
一般工业技术   7420篇
冶金工业   22946篇
原子能技术   626篇
自动化技术   9858篇
  2024年   168篇
  2023年   742篇
  2022年   1004篇
  2021年   1476篇
  2020年   1054篇
  2019年   912篇
  2018年   1466篇
  2017年   1802篇
  2016年   1977篇
  2015年   2035篇
  2014年   2048篇
  2013年   2415篇
  2012年   4240篇
  2011年   4781篇
  2010年   2650篇
  2009年   2577篇
  2008年   2347篇
  2007年   2262篇
  2006年   2366篇
  2005年   4981篇
  2004年   3652篇
  2003年   2985篇
  2002年   1720篇
  2001年   1491篇
  2000年   1153篇
  1999年   1645篇
  1998年   6944篇
  1997年   4517篇
  1996年   3202篇
  1995年   2016篇
  1994年   1533篇
  1993年   1445篇
  1992年   513篇
  1991年   501篇
  1990年   450篇
  1989年   405篇
  1988年   405篇
  1987年   284篇
  1986年   244篇
  1985年   190篇
  1984年   85篇
  1983年   95篇
  1982年   157篇
  1981年   187篇
  1980年   199篇
  1979年   61篇
  1978年   98篇
  1977年   614篇
  1976年   1321篇
  1975年   99篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
针对加油站在油品进、销、存方面因管理和人为作弊而产生的损耗大问题,提出了解决办法:各环节交接手续要严密完备;发货方实施保量运输,选择信誉好的承运方;在销售、储存方面应加强管理,推行加油站计量员、账务员集中管理,主要账表电子表格化,及时上报主管部门,执行责任追究制并与效益工资挂钩。  相似文献   
62.
63.
罗子丽 《电子质量》2006,(10):51-52
本文从科学、规范和监管三个方面出发,对提高认证有效性提出了几点建议.  相似文献   
64.
The expression of cytokeratins (CK), involucrin, vimentin, CD34, and alpha-smooth-muscle actin was studied in fetal and adult hair follicles. The first stage of the developing hair follicle is characterized by palisaded, elongated epithelial cells budding from the epidermal basal layer. These cells express CK5/6, CK14, CK17, CK19, and vimentin. During the following weeks of gestation, different structures in the developing hair follicle can be identified and characterized. The matrical cells display only CK19. The keratinocytes of the outer root sheath express CK5/6, CK14, CK17, CK19, and involucrin; those of the inner root sheath, CK4, CK18, and involucrin; those of the isthmus, the same profile as the ORS. In the infundibulum, the basal-layer keratinocytes express CK5/6, CK14, CK17, and CK19, whereas in the suprabasal layers CK1, CK4, CK10, CK14, and CK17 are seen. The adult hair follicle in anagen fails to express CK19 in the matrical cells and isthmus and both CK17 and CK19 in the infundibulum. These profiles of intermediate filaments and other markers appear to be potentially useful in categorizing neoplasms with apparent follicular differentiation.  相似文献   
65.
66.
Phospholamban (PLN) was expressed in Escherichia coli as a protein fusion with glutathione S-transferase (GST). GST-PLN was mostly present in the insoluble protein fraction and accounted for approximately 50% of total insoluble protein. Attempts to suppress inclusion body formation or to use GST as an affinity-purification tag failed. A successful purification method is based on preparative SDS/PAGE and electrodialysis. From 1 g cells we typically purified 13.5 mg fusion protein with a PLN content of 2.8 mg. We genetically inserted an enterokinase (EK) protease site just in front of the PLN sequence and demonstrated the proteolytical liberation of PLN from the carrier protein. The approach described represents a substantial advancement in PLN expression and purification.  相似文献   
67.
We report a 20 month old female patient with diploid-triploid mixoploidy (46,XX/69,XXX) syndrome with hypothyroidism and precocious puberty. The triploid cell line was only expressed in the fibroblast culture and comprised the majority (95%) of the cells. Chromosome analysis of the fetal blood sample and peripheral blood sample were normal. The patient shows typical features of full triploidy (growth and severe mental retardation, cranial and facial dysmorphism, complete syndactyly of fingers 3/4, partial syndactyly of toes 2/3) and facial but no body asymmetry. At the age of 5 months central hypothyroidism and precocious puberty were diagnosed. Thin pigmented streaks were visible on the wrists and legs of the patient at the age of 16 months. This is the first patient reported so far with 46,XX/69,XXX mixoploidy suffering from hypothyroidism and precocious puberty.  相似文献   
68.
69.
Protective immunity against infection with Mycobacterium tuberculosis is imparted by T cells rather than antibodies, but B cells can play a role as antigen-presenting cells and in granuloma formation. We re-evaluated the role of B cells in the course of tuberculous infection in mu-chain knock-out (Ig-) mice. Surprisingly, the organs of M. tuberculosis-infected Ig- mice were found to have three- to eight-fold elevated counts of viable bacilli compared with normal littermates at 3-6 weeks post-infection. Splenic interferon-gamma responses to whole antigen were unimpaired, whilst proliferation to certain mycobacterial peptides was found to be diminished. However, bacille Calmette-Guérin (BCG) vaccination significantly reduced the infection in Ig- mice. The mechanisms by which B cells can influence primary tuberculous infection need further study.  相似文献   
70.
Laparoscopic retroperitoneal lymph node dissection is a new surgical procedure used to enhance staging in men with clinical stage I nonseminomatous germ cell tumors of the testis. The procedure has been performed in a limited number of patients at several centers with extensive laparoscopic experience. Laparoscopic retroperitoneal lymphadenectomy is a technically demanding procedure which can be successfully completed in the majority of patients. However, the risk of complications is greater than in patients who undergo standard open retroperitoneal lymph node dissection. The primary advantage of a laparoscopic approach is shortened hospitalization and rapid return to normal activity. The role of laparoscopy in the management of patients with testis malignancy has not been defined. The use of this staging procedure may help minimize the need for surveillance studies following surgery and may be best utilized in men with a lower likelihood of nodal metastases. Ultimately, prospective study in large groups of patients will be necessary to determine the role of laparoscopic retroperitoneal lymph node dissection in patients with testis cancer.  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