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   1712篇
  免费   135篇
  国内免费   1篇
  1848篇
  2023年   37篇
  2022年   17篇
  2021年   30篇
  2020年   29篇
  2019年   37篇
  2018年   59篇
  2017年   55篇
  2016年   96篇
  2015年   80篇
  2014年   102篇
  2013年   232篇
  2012年   106篇
  2011年   142篇
  2010年   159篇
  2009年   89篇
  2008年   65篇
  2007年   24篇
  2006年   38篇
  2005年   19篇
  2004年   27篇
  2003年   17篇
  2002年   16篇
  2001年   17篇
  2000年   10篇
  1999年   8篇
  1998年   15篇
  1997年   8篇
  1996年   16篇
  1995年   14篇
  1994年   13篇
  1993年   22篇
  1992年   21篇
  1991年   15篇
  1990年   12篇
  1989年   7篇
  1988年   12篇
  1985年   14篇
  1984年   11篇
  1983年   12篇
  1982年   11篇
  1981年   9篇
  1980年   10篇
  1979年   8篇
  1978年   10篇
  1977年   11篇
  1976年   6篇
  1975年   9篇
  1974年   8篇
  1972年   11篇
  1971年   8篇
排序方式: 共有1848条查询结果,搜索用时 9 毫秒
171.
172.
Summary The distribution of the mRNAs for chromogranin A and B was analyzed by in situ hybridization with 35S-labeled oligonucleotide probes in formalin-fixed paraffin-embedded carcinoid tumor tissues. All the 15 mid-gut carcinoid tumors examined contained both mRNAs for chromogranin A and B at high level in tumor cells. Sixteen of 18 bronchial carcinoid tumors but only 2 of 5 rectal carcinoid tumors expressed one or both species of chromogranin mRNAs. The same tendency was seen with the argyrophil reaction according to Grimelius where most of the mid-gut tumor cells were uniformly stained, while considerable variation in reactivity was seen in some of the bronchial and rectal carcinoid tumor cells. The sequential sections were stained with a monoclonal antibody against chromogranin A and a polyclonal antiserum which reacts with both chromogranins. The expression of the mRNA for chromogranin A on the carcinoid tumors was almost concordant with that of chromogranin B as well as with the chromogranin A protein, whereas almost all tumors stained positively with the polyclonal antibodies. Analyses of mRNA expression of chromogranin A before and after interferon therapy on 4 patients with mid-gut carcinoids indicated an inhibition at pre-translational level. In conclusion, the mRNAs for chromogranin A and B are good markers for the carcinoid tumors, especially of mid-gut origin. Fore-gut, mid-gut and rectal carcinoid tumors are different in their endocrine properties regarding the expression of the chromogranins.  相似文献   
173.
1. We hypothesised that adult insects actively monitor potential habitats for the presence of fish by means of chemical cues and avoid sites that pose significant risks. This was examined by quantifying colonisation of insects in outdoor pools with no fish (controls), fish (direct predation effect) or caged fish (chemical predator cues).
2. A significant direct effect of predation was found, but no indirect effect (avoidance of chemical cue pools), on the total biomass of colonising insects. However, predatory insects avoided fish-cue pools, thus releasing non-predatory insects from predation. This resulted in significantly greater biomass of non-predatory insects in fish-cue pools than control pools.
3. Fish reduced the number of species of colonising insects in pools through predation. This negative influence of fish implies that caution is necessary when stocking wetlands and ponds with fish if the goal is to maximise biodiversity.
4. Our data suggest that although predatory aquatic insects may use chemical signals to assess the quality of potential habitats with respect to predation risk, direct predation is the main method by which fish affect insect assemblages in ponds. Because fish and invertebrate predators may both have strong effects on prey mortality, behavioural adjustment by insects to the actual predator regime within a habitat should be more important than avoiding colonisation of habitats with fish.  相似文献   
174.
175.
Summary Specially in stress conditoin, some hyaline droplets occur in the perikarya of the neurosecretory hypothalamic cell of Zoarces viviparus. They first appear as filamentous macromolecular material in the intracisternal space, then tend to accumulate in the form of irregular electron dense rods or reticulum. The neurosecretory cells containing such hyaline bodies have usually few elementary neurosecretory granules and dilated endoplasmic reticulum.Aided by a Grant from NATO and the Deutsche Forschungsgemeinschaft.My thanks are due to Prof. Dr. E. Lindner and Doz. Dr. K. H. Andres for their kind help in the explanation of electronmicrographs.  相似文献   
176.
177.
A package of methods and an experimental set-up for the analysis of dynamics of electrical signals from the brain. The methods described and discussed in this study allow detailed and multipurpose analysis of brain potentials both in the time and frequency domains. Special emphasis is given to a new computer-method introduced in this study: A posteriori selective averaging. The selective averaging method is compared with Wiener Filter Estimation of Evoked Potentials.  相似文献   
178.
Tectidrilus probus sp.n. and Tectidrilus profusus sp.n. are described from offshore localities in southern California. Both species appear closely related to T. diversus Ersëus, 1982, which occurs in the same area, but they differ from the latter by possessing small oesophageal diverticula; T. probus differs also by its very small spermathecal vestibules. Tectidrilus profusus is a highly apomorphic form with elaborate, partly muscular, male ducts and spermathecae. Monophyly of Tectidrilus is supported by the short clitellum and the unisetal 'bundles' in postclitellar segments. Patterns of apomorphic character states within the genus are analyzed under the principle of Camin-Sokal parsimony (irreversibility of character states), giving three equally parsimonious cladograms. In the strict consensus tree of these cladograms, eight of the twelve members of Tectidrilus form an apomorphic group defined by the papillated body wall, but the individual species within this group cannot be unequivocally resolved from each other.  相似文献   
179.
A total of 28 species of marine Oligochaeta (belonging to the families Naididae, Tubificidae and Enchytraeidae) are reported from eulittoral and sublittoral sediment samples taken in the Koster area on the Swedish West Coast. Lumbricillus algensis sp.n. and Grania ovitheca sp.n. are described and their morphological and taxonomical relations to other enchytraeids are discussed. L. algensis is characterized mainly by its spermathecae, which project into segment VI, and by its very large penial bulbs. G. ovitheca possesses no dorsal setae, the ventral setae being present posterior to the clitellum only, and its spermathecae consist of a narrow duct and a large egg-shaped to oval ampulla, filling most of the coelom of segment V. Four sublittoral species, Limnodriloides barnardi (Tubificidae), Lumbricillus semifuscus, Marionina sublitoralis and Grania roscoffensis (all Enchytraeidae) are reported as new to the Swedish fauna.  相似文献   
180.
Quarter samples of foremilk and residual milk were taken approximately every second week from 2 days post partum (pp) throughout lactation month 9, from 5 dairy cows in their second lactation period. Bacteriologically positive milk samples were excluded. The aim was to study the variation in total and differential leukocyte counts, N-acetyl-ß-D-glucosaminidase (NAGase), antitrypsin (ATR) and serum albumin (BSA) in milk during the lactation period and different stages of oestrous cycle. Also the between milkings variation was studied from lactation month 4 to 9. At 2 days pp, each fraction of milk contained significantly higher numbers of leukocytes and had a higher activity of NAGase and ATR than later in the lactation period. In foremilk the highest content of BSA was also recorded at 2 days pp. From lactation month 2 to 9, stage of lactation had, in general, a slight effect on the variation in the variables measured. The total leukocyte count in residual milk tended to increase as lactation proceeded. The proportion of monocyte-macrophages in foremilk was significantly decreased during the last 4 months. NAGase and BSA in both fractions and ATR in residual milk increased significantly towards the end of the lactation period. From lactation month 4 to 9 the highest recorded ranges of variation between milkings, within quarter and stage of lactation, in the total leukocyte count, proportions of neutrophils, lymphocytes, monocyte-macrophages, NAGase, ATR and BSA in foremilk were 215 × 103ml, 42 %, 34 %, 54 %, 6.68 units, 0.36 units and 0.14 mg/ml respectively. The corresponding figures in residual milk were higher except for the variation in BSA which was slightly lower in residual milk than in foremilk. In residual milk there was a positive correlation between the proportion of neutrophils and the total leukocyte count, when calculated on data from all cows and the entire experimental period. During the oestrous periods, the proportion of neutrophils in residual milk was higher than during the dioestrous periods. Foremilk and residual milk differed in the total as well as the differential leukocyte counts in all the various stages of lactation, whereas the contents of NAGase, ATR and BSA were equal in both fractions. The exception was 2 days pp when the proportions of lymphocytes were equal in both fractions and BSA-significantly higher in foremilk than in residual milk.  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