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   60399篇
  免费   4933篇
  国内免费   31篇
  65363篇
  2022年   414篇
  2021年   855篇
  2020年   528篇
  2019年   638篇
  2018年   832篇
  2017年   773篇
  2016年   1358篇
  2015年   2395篇
  2014年   2516篇
  2013年   3341篇
  2012年   4239篇
  2011年   4246篇
  2010年   2759篇
  2009年   2442篇
  2008年   3534篇
  2007年   3591篇
  2006年   3392篇
  2005年   3421篇
  2004年   3355篇
  2003年   3148篇
  2002年   3118篇
  2001年   713篇
  2000年   535篇
  1999年   732篇
  1998年   865篇
  1997年   599篇
  1996年   602篇
  1995年   591篇
  1994年   572篇
  1993年   596篇
  1992年   535篇
  1991年   467篇
  1990年   389篇
  1989年   405篇
  1988年   402篇
  1987年   340篇
  1986年   341篇
  1985年   396篇
  1984年   445篇
  1983年   374篇
  1982年   459篇
  1981年   410篇
  1980年   363篇
  1979年   240篇
  1978年   294篇
  1977年   285篇
  1976年   237篇
  1975年   216篇
  1974年   236篇
  1973年   220篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
102.
A regimen designed for effective foolproof antituberculosis treatment, acceptable on a routine basis, was applied to all patients newly diagnosed at the Chest Clinic, Hammersmith Hospital, in 1963, 1964, and 1965. During the first three months of treatment patients received daily (six days a week) streptomycin 0.75 g. plus isoniazid 300 mg. plus sodium para-aminosalicylate (P.A.S.) 12 g. The P.A.S. was usually stopped when bacterial sensitivity reports made this possible. For a further 15 months streptomycin 1 g. plus isoniazid 600 mg. was given on three alternate days each week to complete a total of 18 months'' treatment.Of the total of 140 patients (66% sputum-positive) 112 (80%) completed the planned 18 months with intermittent streptomycin plus isoniazid and a further eight completed treatment on alternative regimens (a total of 85%). The equivalent figures for one year are 88% and 94%. Excellent clinical and radiological results, together with sputum conversion, were achieved in 138 of the 140 patients (99%). Only two patients were lost from surveillance, because of failure to co-operate, before quiescence was obtained.It is concluded that the total efficiency of supervised intermittent treatment is greater than that of unsupervised daily regimens. Since 100% arrest of tuberculosis is possible with co-operative patients, less should not be accepted in developed countries.  相似文献   
103.
Appendicitis is not the only common cause of acute abdominal pain in childhood. Almost equally common is an acute episode which in its early stages resembles acute appendicitis but which subsides without treatment in 24 to 48 hours. The clinical features of this syndrome are contrasted with those of appendicitis. The two conditions cannot always be distinguished on clinical grounds, leading to admission to hospital for observation and the finding of a normal appendix in 14% of operations for suspected appendicitis. Reasons are given for abandoning attempts to diagnose acute mesenteric adenitis at the bedside.  相似文献   
104.
Summary Cell differentiation in Anabaena cylindrica is accompanied with characteristic changes in the pigment composition of heterocysts and spores. In both the absence of phycocyanin is consistent with the lack of CO2-fixing ability previously reported. The presence of chlorophyll and -carotene suggests a functional photosystem I in heterocysts. In the spores chlorophyll is largely replaced by pheophytin. The quantitative distribution of carotenoids is also affected. An increase in the proportion of -carotene is characteristic of heterocysts while spores show a larger proportion of xanthophylls compared with the intact filament.  相似文献   
105.
The social behaviour of T. m. includes ritualized fights. Sperm transfer is achieved by means of a spermatophore deposited on the ground and by the male pulling the female over it. The behaviour and the spermatophore are described and compared to those of other arachnids and the phylogenetical implications are discussed.  相似文献   
106.
107.
Zusammenfassung Das Parenchym der peribronchialen Mikroparaganglien wird von zwei Zellarten aufgebaut: Chromaffine Zellen (Typ I-Zellen) und Hüllzellen (Typ II-Zellen).Die chromaffinen Zellen sind durch ihren reichen Gehalt an Vesikeln mit elektronendichtem Inhalt gekennzeichnet, deren Durchmesser 700–1300 Å beträgt. Markfreie Nerven ziehen an die Typ I-Zellen heran und bilden synaptische Kontakte aus. Die chromaffinen Zellen sind dabei der postsynaptische Teil der Verbindung. Die Hüllzellen entsprechen strukturell und funktionell den Schwannschen Zellen.Ein Mikroparaganglion wird von 10 bis 15 chromaffinen Zellen und deren Hüllzellen aufgebaut. Sie liegen dicht um fenestrierte Kapillaren, die von den Aa. bronchiales aus versorgt werden. Die Paraganglien sind von den Nervenzellen des peribronchialen Plexus durch dessen Perineurium getrennt. Selten findet man solitäre chromaffine Zellen innerhalb der Nervengeflechte. Es wird angenommen, daß die Paraganglien endokrine Funktionen erfüllen.
The fine structure of the guinea pig peribronchial micro-paraganglia
Summary The parenchyma of peribronchial microparaganglia consists of two different cell types: chromaffin cells (type I-cells) and surrounding cells (type II-cells).The chromaffin cells contain numerous vesicles with electron dense content, their diameter ranging from 700 to 1,300 Å. Unmyelinated nerves form synapses with type I-cells. The surrounding cells structurally and functionally correspond to Schwann cells.A micro-paraganglion consists of ten to fifteen chromaffin cells and their satellite cells. They are situated close to fenestrated capillaries, which are supplied from the Aa. bronchiales. A perineurial sheath separates the paraganglia from the nerve cells of the peribronchial plexus. Single chromaffin cells are found seldom within the nervous plexus.The paraganglia are thought to have an endocrine function.
  相似文献   
108.
Summary Budding bacteria from aquatic or terrestrial habitats were found to accumulate ferric oxide hydrate (ferric hydroxide) on their cell surfaces. Metal paper clips served as the source of oxidizable iron. Pure cultures deposited ferric hydroxide during growth on sea water medium at a pH of 7.8, but not in a mineral salts medium of normal ionic strength, of pH 7.2, and without NaCl, although some active strains came from fresh water or soil.Ferric iron deposition was found to be initiated at primary active sites on the cell surface; the hyphae and rods eventually become completely encased by the heavy coat.The presence of iron depositing, budding bacteria in fresh water, brackish water or sea water indicates an ubiquitous distribution of these microorganisms.Actively depositing isolates from marine environments are more closely related to Pedomicrobium than to Hyphomicrobium spp. because of their multiple formation of hyphae from rod-shaped swarmer cells. A taxonomic and cultural study of these new forms is in progress.  相似文献   
109.
Zusammenfassung Junges Submersmycel von Aspergillus niger ist in seiner 14C-Saccharoseinkorporation uneinheitlich. Weiterhin konnte gefunden werden, daß die Saccharoseaufnahme gleichmäßig über die Hyphen junger Pellets erfolgt. Eine verstärkte radioaktive Markierung der Hyphenspitze nach längerer Inkubation ist die Folge des Spitzenwachstums. Altes Mycel verhält sich anders. Hier sind Orte intensiven Stoffwechsels proliferierende Conidienträger.
On the localization of the sucrose uptake by submerged Aspergillus niger mycel
Summary It was found, that joung pellets of Aspergillus niger are inhomogen in relation to the incorporation of 14C-sucrose. In joung pellets the uptake takes place uniformly over the surface of the hyphae. With extending of the incorporation time the radioactivity was localized mainly in growing tips of the hyphae. Growth centres in old pellets are not the hyphae but the proliferating conidiophores.
  相似文献   
110.
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