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   3145篇
  免费   35篇
  国内免费   14篇
电工技术   42篇
综合类   28篇
化学工业   64篇
金属工艺   7篇
机械仪表   104篇
建筑科学   15篇
矿业工程   6篇
能源动力   8篇
轻工业   355篇
水利工程   2篇
无线电   15篇
一般工业技术   102篇
冶金工业   2327篇
原子能技术   3篇
自动化技术   116篇
  2022年   17篇
  2020年   18篇
  2019年   30篇
  2018年   6篇
  2016年   4篇
  2014年   7篇
  2013年   155篇
  2012年   31篇
  2011年   22篇
  2010年   31篇
  2009年   31篇
  2008年   30篇
  2007年   35篇
  2006年   22篇
  2005年   24篇
  2004年   23篇
  2003年   22篇
  2002年   15篇
  2001年   6篇
  2000年   10篇
  1999年   80篇
  1998年   758篇
  1997年   436篇
  1996年   287篇
  1995年   157篇
  1994年   126篇
  1993年   150篇
  1992年   26篇
  1991年   33篇
  1990年   42篇
  1989年   40篇
  1988年   40篇
  1987年   54篇
  1986年   38篇
  1985年   38篇
  1984年   10篇
  1983年   6篇
  1982年   13篇
  1981年   22篇
  1980年   19篇
  1979年   9篇
  1978年   5篇
  1977年   60篇
  1976年   125篇
  1975年   6篇
  1973年   5篇
  1969年   5篇
  1958年   4篇
  1955年   18篇
  1954年   16篇
排序方式: 共有3194条查询结果,搜索用时 15 毫秒
21.
22.
To determine whether chromosome analysis could facilitate the diagnosis of malignant pleural effusions, we examined chromosomes in effusions from 104 unselected patients. An effusion was regarded as malignant if at least three of 30 metaphase cells were hyperdiploid or contained a marker chromosome. Results were compared with standard cytologic diagnoses. All 22 benign effusions were diagnosed correctly by cytologic examination, but one nosed correctly by cytologic examination, but one (acute rheumatoid lung disease) was misclassified as positive by chromosome criteria. Of the 82 malignant effusions, 53 (65 per cent) were diagnosed correctly by cytologic tests, as compared with 58 (71 per cent) by chromosome analysis (P greater than 0.2). Among patients with malignant neoplasms, 13 had leukemia or lymphoma; only four of these (31 per cent) were diagnosed by cytologic tests as compared with 11 (85 per cent) by chromosome analysis (P less than 0.01). The combination of standard cytologic and chromosome analyses correctly identified 83 per cent of the neoplasms, a result significantly better than that with either technic alone (P less than 0.01).  相似文献   
23.
A total of 98 colposcopically directed biopsies were obtained from the vagina, cervix, and cervicovaginal ridge (hood) of 80 young women believed to have had intrauterine exposure to stilbestrol (DES). Specific investigation of the patient's medical records corroborated the history of maternal stilbestrol administration in 36 patients (45%), while in the remainder the drug history was regarded as presumptive since medical records were unavailable for review. The findings did not differ significantly in those biopsies taken from patients with confirmed or presumptive drug histories. Histologic evidence of vaginal adenosis was detected in vaginal biopsies from 43 patients. In 30 cases (70%) benign Müllerian-type glandular epithelium was in the superficial vaginal wall, residing on the mucosal surface and/or in the lamina propria. The glandular epithelium predominantly was of endocervical type, but in six instances it resembled endometrial or fallopian tubal epithelium. The glands were accompanied by varying degrees of squamous metaplasia in 22 cases. When extensive the metaplasia produced transformation zones similar to those seen in the normal cervix. Vaginal biopsies of adenosis from the other 13 patients (30%) revealed squamous metaplasia without demonstrable glands due to complete transformation of all antecedent glandular epithelium by squamous metaplasia. Our studies indicate that squamous metaplasia is a component of major importance in the natural history of adenosis and that the concept of adenosis should be broadened to include those examples comprised exclusively of metaplastic epithelium. In such examples metaplasia is identified by the immaturity and poor glycogenation of the squamous cells and their accompanying squamous pegs which often contain residual gland openings or squamous "eddies." Similar findings were present in biopsies of seven cervicovaginal ridges and in cervical biopsies from 37 patients, except for the absence of endometrial or tubal type glands in the latter site. Although no adenocarcinomas were detected, six patients had squamous dysplasia of the vagina and/or cervix. In no case were premalignant or dysplastic changes of glandular cells found. Our findings support the thesis that stilbestrol-associated adenosis represents anomalous embryologic localization of the original squamocolumnar junction in the vagina rather than in the cervix. It is closely related to so-called cervical "erosions." The development of squamous metaplasia accounts for modifications in the clinical and histologic appearances by producing transformation zones which then may be subject to the same oncogenic stimuli for squamous neoplasia as are their counterparts in the cervix.  相似文献   
24.
Eggs of Schistosoma mansoni were obtained from livers of mice and hatching was observed under varying conditions of light and ionic composition of the medium. Hatching occurred equally well in light and in darkness. Eggs also hatched readily in 1- to 50-m OsM solutions of urea, sucrose, sodium chloride, and glycerol, but hatching was inhibited at higher concentrations unless the eggs were left in solutions for long periods of time. Hatching readily occurred in deionized water, but the emerged miracidia did not swim longer than 5 to 10 min unless Na+ was added. Histochemistry of the egg showed DNA-positive egg granules and a polysaccharide-positive vacuole matrix. Acid mucopolysaccharides were stained in the vacuolar matrix and in the anterior sac of the miracidium. Longitudinal alignment of constituents of the egg shell is suggested by the predominance of longitudinal rents in the shell at hatching. A mechanism of hatching involving an osmotic stimulus is proposed.  相似文献   
25.
26.
27.
Progesterone and oestrone alone or in combination were administered to sows during early gestation. A dose of 25 mg progesterone and 12-5 mug oestrone injected together for 10,5 or 2 consecutive days during the implantation interval caused increased litter size at term.  相似文献   
28.
Protein(s) have been found in a wide range of tissues which have a high affinity for 25-hydroxycholecalciferol. Of the tissues examined only erythrocytes do not have this protein. The properties of the protein have been examined and it has been found that the association constatns range from 2 - 10(9) to 5 - 10(9) M-1 and the sedimentation constants between 5.0 and 6.0 S. It was not possible to distinguish the proteins from the different tissues by their S values, mobility on gel electrophoresis or behaviour on ion-exchange chromatography. These techniques were all used, however, to show that the tissue 25-hydroxycholecalciferol binding protein is distinct from the main plasma binding protein for this steroid and from the intestinal 1,25-dihydroxycholecalciferol-binding protein. A protein has been in the plasma of rachitic animals but not of normals, which is apparently indistinguishable from this new tissue 25-hydroxycholecalciferol-binding protein. The steroid specificity of this new binding protein has been shown to be dependent upon a C-25 hydroxyl group, and an intact conjugated double bond system. Possible functions for this protein have been briefly discussed.  相似文献   
29.
介绍了卷烟信息网络防伪管理系统构建原理、技术特点和功能 ,及其在烟草行业中的应用。  相似文献   
30.
Milk samples were collected in the dry season ( n =  155) and in the rainy season ( n =  68) to establish a correlation between electronic flow cytometry and standard plate count for the determination of total bacterial count of raw milk. Results were expressed in individual bacterial count (ibc) and colony forming unit (cfu) for electronic flow cytometry (Bactocount) and standard plate count, respectively. The accuracy of Bactocount, denoted by the residual standard deviation ( s ( y,x )), was 0.309 log cfu/mL. The predictive interval of estimated values was broad and it is suggested that total bacterial count should be expressed in ibc without transformation to cfu.  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