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   43532篇
  免费   3925篇
  国内免费   33篇
  47490篇
  2023年   168篇
  2022年   313篇
  2021年   600篇
  2020年   401篇
  2019年   494篇
  2018年   646篇
  2017年   558篇
  2016年   1049篇
  2015年   1765篇
  2014年   1886篇
  2013年   2462篇
  2012年   2998篇
  2011年   3070篇
  2010年   1961篇
  2009年   1681篇
  2008年   2535篇
  2007年   2519篇
  2006年   2285篇
  2005年   2351篇
  2004年   2299篇
  2003年   2200篇
  2002年   2144篇
  2001年   516篇
  2000年   428篇
  1999年   516篇
  1998年   615篇
  1997年   473篇
  1996年   417篇
  1995年   400篇
  1994年   365篇
  1993年   356篇
  1992年   409篇
  1991年   345篇
  1990年   280篇
  1989年   283篇
  1988年   283篇
  1987年   261篇
  1986年   244篇
  1985年   312篇
  1984年   322篇
  1983年   262篇
  1982年   354篇
  1981年   283篇
  1980年   258篇
  1979年   193篇
  1978年   223篇
  1977年   210篇
  1976年   179篇
  1974年   192篇
  1973年   199篇
排序方式: 共有10000条查询结果,搜索用时 5 毫秒
101.
102.
The different types of recrystallization which can be observed in the Triassic involutinids should be considered in the taxonomic treatment of this foraminiferal family. If the diagenetic modifications of the test are neglected the same form could be placed into different suborders. Our inclusion of the genusTriasina Majzon in the Involutinidae proposed earlier on purely morphologic grounds, seems to be supported by the fact that the same types of recrystallization exist inTrocholina, Involutina undTriasina.  相似文献   
103.
During two years of passage, several myxamoebal strains of Physarum polycephalum changed with regard to their properties in crosses and plaque morphology. These changes have been correlated with increased nuclear deoxyribonucleic acid content.  相似文献   
104.
Selective esterification reactions of 1,6-anhydro-3-deoxy-β-D-xylo-hexopyranose(1), 1,6-anhydro-β-D-glucopyranose (7), and several derivatives of 7, were conducted with an acid chloride or acid anhydride in pyridine. Reaction of 1 with p-toluenesulfonyl chloride and with benzoyl chloride gave 70 and 63%, respectively, of the 2-esters. The 2-methyl and 2-benzyl ethers of 7, both having strongly hydrogen-bonded C-4 hydroxyl group, reacted with p-toluenesulfonyl chloride to yield the 4-monosulfonates (71 and 74%, respectively). Esterification of the 2-methyl ether and 2-p-toluenesulfonate of 7 with p-toluenesulfonic anhydride instead of with p-toluenesulfonyl chloride led to increased yields of the 4-p-toluenesulfonates after a shorter reaction-time.  相似文献   
105.
106.
107.
Serial passage of the 64-2389 strain of type 3 parainfluenza virus in cercopithecus monkey kidney tissue cultures at low temperatures resulted in the selection of a variant which had a higher efficiency of plaque formation at 25 C than the parent line grown at 37 C. The cold variant, unlike the parent strain, plaqued readily at 25 C, and at 37 C it produced significantly larger plaques. Virus titers of the cold variant in hamster lungs were significantly lower and this was probably caused by the stimulation of interferon by the cold variant during the early phase of the infection. The cold variant, like the virus grown at 37 C, also induced the synthesis of interferon late in the infection. Hamsters responded to the intranasal inoculation of each virus line by the development of hemagglutinating-inhibiting antibodies in the sera.  相似文献   
108.
Zusammenfassung Die Epithelzellen der Plexus chor. ventr. III und IV, das Paraphysenepithel und das Ventrikelependym von Rana temporaria L. zeigen eine deutliche — wenn auch quantitativ unterschiedliche — Aktivität von SDH, -HBDH und LDH. Der Nachweis einer UDPGGT-Aktivität fällt dagegen nur im Plexusepithel positiv aus. In der Plexusepithelzelle sind die Formazangranula gleichmäßig über das gesamte Plasma verteilt, während sie in den Ependymzellen vorwiegend im apikalen, lumenwärtigen Teil der Zelle angeordnet sind. Die Ependymzellen lassen im Reaktionsausfall Typenunterschiede erkennen. Bei einigen Tieren wird die Auswirkung einer Adrenalininjektion auf das Enzymmuster der Plexusepithelzellen untersucht; die funktionellen Zusammenhänge mit einer gleichzeitigen Entspeicherung ihres Glykogenvorrats werden erörtert. Die Verteilung und der Lamellierungstyp der Mitochondrien im Plexus- und Paraphysenepithel werden mit elektronenmikroskopischen Aufnahmen illustriert. Einige Komentare sind dem histochemischen Verhalten des Wundrandes gewidmet.
Histochemical studies on the choroid plexuses, the paraphysis cerebri, and the ependyma of Rana temporaria L.
Summary The epithelium of the choroid plexuses of the IIIrd and IVth ventricles as well as the paraphyseal epithelium and the ventricular ependyma cells of Rana temporaria L. show distinct activities of SDH, -HBDH and LDH, that differ quantitatively. The UDPGGT-reaction is positive in the plexus epithelium. In the epithelium of the choroid plexus, the formazan granules are evenly distributed in the cytoplasm. In the ependyma cells an apical accumulation of this material can be demonstrated. The various morphological types of the ependyma cells differ in the intensity of the SDH, -HBDH and LDH-reactions. In the plexus cells of some animals the effect of epinephrine was studied on the histochemically-detectable activity of these enzymes with respect to the simultaneous depletion of the glycogen depot. The distribution and ultrastructure of mitochondria is described in the choroid plexus and paraphyseal epithelial cells. A comment is made in reference to some histochemical pecularities of stab wound areas.


Teil einer medizinischen Doktorarbeit.

Mit Unterstützung durch die Deutsche Forschungsgemeinschaft.  相似文献   
109.
Often patients in whom there is little to suggest myxedema or cretinism have subclinical hypothyroidism. Once the condition is suspected, it can be diagnosed by determination of protein-bound iodine and, if the PBI is low, by response to therapy with thyroid hormone.Patients in the following categories should have protein-bound iodine determination: Those having (1) a history of previous treatment for hypothyroidism; (2) suboptimal development in children; (3) ovarian dysfunction, infertility, habitual abortion or unusual menopausal disorders; (4) symptoms of malaise and debility, such as undue fatigue, somnolence, mental asthenia and anxiety; (5) unexplained anemia; (6) colloid goiter, adenomatous goiter and cancer of the thyroid gland.If hypothyroidism is diagnosed, administration of thyroid hormone in increasing amounts, as determined by serial serum PBI tests, should be carried out indefinitely. Instruction of the patient is essential.  相似文献   
110.
Although Montreal is in an endemic area, significant clinical histoplasmosis with systemic manifestations has been, until recently, infrequently diagnosed. However, since the autumn of 1963, 31 cases of clinically significant histoplasmosis have been seen by the authors. These were divided into two groups: (1) patients in whom the diagnosis was established on the basis of histological and/or cultural demonstration of the fungus; (2) patients in whom the diagnosis was based on a positive histoplasmin skin test, a complement fixation antibody titre of 1:32 or greater and compatible clinical and radiological findings. An additional group of 11 patients who presented with erythema multiforme was investigated and a heretofore unrecognized relationship between histoplasmosis and erythema multiforme was established.  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