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   10255篇
  免费   844篇
  国内免费   843篇
  2024年   13篇
  2023年   123篇
  2022年   133篇
  2021年   279篇
  2020年   322篇
  2019年   413篇
  2018年   384篇
  2017年   367篇
  2016年   371篇
  2015年   389篇
  2014年   657篇
  2013年   794篇
  2012年   505篇
  2011年   568篇
  2010年   488篇
  2009年   491篇
  2008年   602篇
  2007年   583篇
  2006年   477篇
  2005年   461篇
  2004年   356篇
  2003年   332篇
  2002年   258篇
  2001年   229篇
  2000年   204篇
  1999年   187篇
  1998年   174篇
  1997年   147篇
  1996年   141篇
  1995年   104篇
  1994年   109篇
  1993年   137篇
  1992年   108篇
  1991年   111篇
  1990年   79篇
  1989年   79篇
  1988年   85篇
  1987年   71篇
  1986年   55篇
  1985年   74篇
  1984年   88篇
  1983年   47篇
  1982年   61篇
  1981年   53篇
  1980年   59篇
  1979年   50篇
  1978年   35篇
  1977年   19篇
  1976年   26篇
  1972年   13篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
海城小孤山的骨制品和装饰品   总被引:11,自引:5,他引:6  
小孤山的骨制品包括鱼叉、标枪头和骨针,它们在工艺上与欧洲旧石器时代晚期、尤其是马格德林文化的制品十分相似。小孤山的骨针和山顶洞的骨针相似,但工艺水平稍高。小孤山的装饰品包括穿孔牙齿和蚌壳,它们与山顶洞的同类制品基本一致,但穿孔技术稍高。小孤山含上述制品的堆积物的时代为晚更新世,年代测定的初步结果为距今40,000—20,000年左右。  相似文献   
102.
Receptors for thyrotropin-releasing hormone (pGlu-His-Pro-NH2, TRH) on thaw-mounted sections of rabbit spinal cord have been identified biochemically and visualized by light microscopic autoradiography. Binding of [3H] [3-Me-His2]TRH to 20 microns sections exhibited high apparent affinity and a pharmacological specificity almost identical to that previously demonstrated for spinal TRH receptors in membranes. In autoradiograms, the highest density of TRH receptors appeared in the substantia gelatinosa of the dorsal gray and around the central canal, with intermediate levels in the ventral gray.  相似文献   
103.
Observations on the separation of Theileria sporozoites from ticks   总被引:3,自引:0,他引:3  
Hyalomma anatolicum anatolicum ticks infected with Theileria annulata were partially fed on rabbits and then ground up with tissue culture medium. The ground up ticks were treated by centrifugation at 100 g, filtration through membranes of 8 μm pore diameter and centrifugation on a discontinuous density gradient of Percoll. Counts of sporozoites and tick debris were made from Giemsa stained slides of samples at each stage of the separation. Debris was removed during light centrifugation and filtration at a greater rate than sporozoites. After filtration approximately 41% of the original sporozoites remained in the suspension. After density gradient centrifugation most sporozoites were found in a distinct zone, at approx. 1·08 g/cm3 density, separate from most dense debris and light debris and soluble contaminants. After this final centrifugation approximately 24% of the original sporozoites remained in the recovered suspension.  相似文献   
104.
Human monocyte-macrophages in culture express specific receptors for low density lipoproteins (LDL receptor) and human acetylated LDL (AcLDL receptors or scavenger receptors). After 24 h in lipoprotein-deficient serum, the cells expressed 2-3 fold more AcLDL receptors than LDL receptors as measured by trypsin releasable radioactivity after exposure to 125I-LDL or 125I-AcLDL at 37 degrees C. The efficiency of intracellular ligand delivery by the two receptors was evaluated as an internalization index (defined as intracellular + degraded/bound ligand). This index was several fold greater for 125I-AcLDL than for 125I-LDL, in the same cells exposed to either ligand under identical conditions. These results suggest that the scavenger receptors recycle more rapidly than do LDL receptors.  相似文献   
105.
Long bone growth is analyzed for 180 children from a Medieval population at Kulubnarti in Sudanese Nubia (550–1450 A.D.). A regional interpopulation comparison is made with growth data from Wadi Halfa in Lower Nubia, and an intrapopulation analysis is undertaken to assess diachronic changes in growth at Kulubnarti. Changes in growth patterns are interpreted in the context of mortality and morbidity profiles and relationships between the three variables are discussed. It is suggested that changes in the sociopolitical environment may have been responsible in part for altering levels of biological stress and impacting growth.  相似文献   
106.
R. Keren  A. Meiri  Y. Kalo 《Plant and Soil》1983,74(3):461-465
Summary The response of the cotton plant (Gossypium hirsutum L.) to 9.0 and 12.5 cm intra- and 75.0 and 96.5 cm inter-row spacing was studied under irrigation with saline water (5.5 dS/m, SAR 18). In general, the dry weight per plant matter, the leaf area, number of bolls and flowers, and yield per plant were all affected significantly by intra-row spacing but, not by inter-row spacing. However, on a unit area basis, they were affected only by the inter-row spacing. This indicates that competition between plants exists when intra-row spacing is reduced, whereas no significant competition occurs due to a decrease in the inter-row spacing. Although the effect of intra-row spacing on yield for a unit area was found to be not significant, the effect of inter-row spacing was significant. Yield in plots with the conventional spacing (96.5 cm between rows and 12.5 cm between plants in the row) was 4863 kg/ha, whereas the yield in plots with 75 cm between rows was about 23% higher (5974 kg/ha). The lint percentage and the plant height were not affected significantly by either intra- or inter-row spacings.Contribution from the Institute of Soils and Water, Agricultural Research Organization, The Volcani Center, Bet Dagan 50250, Israel. No.676-E, 1983 series.  相似文献   
107.
Parenchymal cells, isolated from untreated (control), phenobarbital(PB)-or 3-methylcholanthrene(3-MC)-treated rats, were separated into four subpopulations according to cell density, and glucuronidation and sulfation of p-nitrophenol (PNP) in the hepatocyte subpopulations were investigated. PB enhanced the glucuronidation almost 2-fold but not the sulfation, while 3-MC enhanced both glucuronidation (3-fold) and sulfation (2-fold) in the original cell suspensions. Some gradation trends were found in the conjugation activities among the hepatocyte subpopulations: In the control experiment, the extent of glucuronidation in four subpopulations was virtually the same but sulfation in high-density hepatocytes was slightly higher than in low-density ones. Both glucuronidation and sulfation were higher in low-density hepatocytes from PB-treated rats, though the gradation was very modest. Glucuronidation and sulfation tended to be slightly higher in middle-density hepatocytes in the 3-MC experiment. However, no definite correlation in conjugation activities vs. cell density, like those seen in cytochrome P-450s vs. cell density in the hepatocytes isolated from PB-treated rats, were found in the subpopulations from control or inducer-treated rats. Simultaneous studies on acetylation of p-aminobenzoic acid (PABA) revealed that the activities in the subpopulations were virtually the same and the inducers had little influence on the activity.  相似文献   
108.
Résumé Le squelette vertébral de l'Anguille est formé d'os cellulaire: lamellaire compact ou spongieux, suivant les différentes parties de la vertèbre. Nous avons pu y mettre en évidence, chez des animaux physiologiquement normaux, les trois catégories de cellules caractéristiques de l'os des vertébrés supérieurs: ostéoblastes, osteocytes, ostéoclastes. Elles ont les mêmes fonctions que chez ces derniers, les ostéoblastes procèdent à l'élaboration du tissu osseux, alors que les ostéoclastes le détruisent; à cette résorption ostéoclastique s'ajoute une lyse périostéocytaire ou résorption périlacunaire. Les osteocytes, dans ce tissu, nous paraissent être des éléments actifs; néanmoins, leur nombre (par unité de surface) est très inférieur à celui trouvé chez les Mammifères. Le remaniement osseux résultant du jeu de l'apposition et de la résorption est important et comparable à celui existant chez l'Homme.L'os de l'Anguille est, à de nombreux points de vue, très voisin de celui des Mammifères; les Poissons n'ont pas de parathyroïdes en tant que telles mais ils sont pourvus d'autres glandes vraisemblablement impliquées dans la régulation phosphocalcique: corps ultimobranchial et corpuscules de Stannius. Notre but sera donc d'essayer de déterminer comment est réglé le métabolisme de l'os cellulaire des Téléostéens.
Histologic study on teleost cellular bone I.
Summary The vertebral skeleton of the eel consists of cellular bone, either lamellar or spongy, depending on different parts of the vertebra. In this osseous tissue we have found, in physiologically normal animals, three categories of caracteristic cells of the bone of higher vertebrates: osteoblasts, osteocytes, osteoclasts. They have the same functions as in higher vertebrates, osteoblasts form the bone while the osteoclasts which are to be found in Howship's lacunae destroy it. In addition, a perilacunar type of bone resorption or osteocytic osteolysis can be observed. In this bone, osteocytes seem to be active cells, but the concentration of osteocytes is decidedly lower than that to be found in Mammals.The osseous remodeling produced by apposition and resorption is of the same importance as in human bone. The bone of the eel, in many ways, closely resembles that of mammals. Teleost fish do not have parathyroid glands, but their phosphocalcic regulation seems to be facilitated by the action of two endocrine glands: Ultimobranchial body and the corpuscles of Stannius.The regulation of the cellular bone metabolism of Teleostean fishes is discussed.
Nous remercions Monsieur le Professeur Baud qui nous accueille dans son laboratoire à Genève et qui nous prodigue ses conseils.  相似文献   
109.
几个生态因子对黄盖鲽的影响   总被引:1,自引:0,他引:1  
毕庶万  郑振虎 《生态学杂志》1989,8(5):19-21,F004
黄盖鲽(Psuedopleuronectes yokohameGünther)是鲽科中的冷温性鱼类,广泛分布在日本、朝鲜及我国的东海、黄海和渤海。地方种群多,洄游范尉小,适应能力强,既是底栖生物食性,又可耐较低的温度,虽非名贵鱼种,却具有一定的经济价值,在开展近海增殖时,不存在越冬和效益外流问题。因此,早在60年代,日本山口县和大分县的学者们,便开始着手该品种的人工孵化和增殖放流试验。80年代初已达年放流2—3cm的稚鱼苗7.0×10~6尾的水平。为了在渤海开展增殖工作,建立综  相似文献   
110.
下肢长骨骨重的非对称性   总被引:4,自引:0,他引:4  
本文测量82副中国成年下股长骨即股骨,胫骨和腓骨的重量,在两侧骨重相差>1%时,则股骨、胫骨和腓骨及其三骨总重均以非对称性为多,均具有非常显著性差异(P<0.001)。除腓骨重具有明显侧别差异外,其余无显著性侧别差异,对腓骨侧差解释为:①腓骨主要机能是肌的附着,而下肢对踢和足趾取物具有明显的侧别差异;②以两侧骨重相差>1%时为非对称性的标准,由于腓骨绝对重量较小,在两侧相差<0.5克时即多属非对称性。  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