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   714篇
  免费   42篇
  756篇
  2023年   8篇
  2022年   9篇
  2021年   29篇
  2020年   15篇
  2019年   12篇
  2018年   16篇
  2017年   16篇
  2016年   23篇
  2015年   34篇
  2014年   36篇
  2013年   52篇
  2012年   52篇
  2011年   51篇
  2010年   26篇
  2009年   24篇
  2008年   22篇
  2007年   22篇
  2006年   23篇
  2005年   17篇
  2004年   15篇
  2003年   16篇
  2002年   11篇
  2001年   8篇
  2000年   9篇
  1999年   4篇
  1997年   6篇
  1995年   2篇
  1992年   2篇
  1991年   4篇
  1987年   4篇
  1985年   33篇
  1984年   21篇
  1983年   14篇
  1982年   32篇
  1981年   23篇
  1980年   11篇
  1979年   10篇
  1978年   5篇
  1977年   3篇
  1976年   4篇
  1975年   4篇
  1974年   3篇
  1973年   4篇
  1972年   2篇
  1970年   3篇
  1969年   3篇
  1965年   2篇
  1964年   2篇
  1945年   1篇
  1943年   1篇
排序方式: 共有756条查询结果,搜索用时 15 毫秒
1.
The investigation of Encelia canescens afforded, in addition to several known compounds, four new dimeric p-hydroxyacetophenone derivatives, two epimeric chromene dimers and two epimeric mixed dimers of euparin and encecalin. Furthermore, derivatives of tremetone and of encecalin were present. The structures were elucidated hy high field 1H NMR spectroscopy.  相似文献   
2.
The investigation of three South African Vernonia species afforded minute amounts of five new glaucolides, two monoepoxides and three diepoxides. The structures were elucidated by 1H NMR spectroscopy. The roots of Vernonia sutherlandii contain, in addition to vernonataloide, bergamotene and santalene, minute amounts of the corresponding acetoxy derivatives.  相似文献   
3.
Allogeneic bone marrow grafts carried out after previous administration of antilymphocytic serum alone were attempted in 16 patients. Of these, six had acute myeloblastic leukaemia, four acute lymphoblastic leukaemia, and one a blast cell crisis in polycythaemia vera. Ten of these patients were in an overt phase of the disease and resistant to chemotherapy, while nine had complete agranulocytosis. In five of these patients erythrocyte and leucocyte antigenic markers demonstrated the establishment of the graft. One patient had thalassaemia major, and four others had aplasia of the bone marrow, in one case due to chloramphenicol poisoning and in another to virus hepatitis. The grafts were successful in the last two patients and transformed their clinical condition.No signs of early acute secondary disease were noted in any of the patients, either when the donor had been given antilymphocytic serum or when he was untreated. The grafts had no adoptive immunotherapeutic effect on the acute leukaemia. These observations have clearly shown that antilymphocytic serum has an immunosuppressive effect in man when it is used alone.  相似文献   
4.
Species identification is pivotal in biodiversity assessments and proteomic fingerprinting by MALDI-TOF mass spectrometry has already been shown to reliably identify calanoid copepods to species level. However, MALDI-TOF data may contain more information beyond mere species identification. In this study, we investigated different ontogenetic stages (copepodids C1–C6 females) of three co-occurring Calanus species from the Arctic Fram Strait, which cannot be identified to species level based on morphological characters alone. Differentiation of the three species based on mass spectrometry data was without any error. In addition, a clear stage-specific signal was detected in all species, supported by clustering approaches as well as machine learning using Random Forest. More complex mass spectra in later ontogenetic stages as well as relative intensities of certain mass peaks were found as the main drivers of stage distinction in these species. Through a dilution series, we were able to show that this did not result from the higher amount of biomass that was used in tissue processing of the larger stages. Finally, the data were tested in a simulation for application in a real biodiversity assessment by using Random Forest for stage classification of specimens absent from the training data. This resulted in a successful stage-identification rate of almost 90%, making proteomic fingerprinting a promising tool to investigate polewards shifts of Atlantic Calanus species and, in general, to assess stage compositions in biodiversity assessments of Calanoida, which can be notoriously difficult using conventional identification methods.  相似文献   
5.
The aerial parts of Baccharis minutiflora afforded in addition to known compounds eight new ent-kaurane derivatives, one being a homo kaurane, while the aerial parts of B. alatemoides gave two pairs of epimeric clerodane derivatives, which, however, had to be modified chemically before they could be separated. The stereochemistry of these diterpenes could not be elucidated with certainty.  相似文献   
6.
An investigation of Brickellia diffusa afforded three new dehydronerolidol derivatives and five new labdane derivatives, all highly oxygenated. The structures were elucidated by spectroscopic methods and a few chemical transformations. The compounds isolated showed close relationships to those isolated from Brickellia sp.  相似文献   
7.
The investigation of two Mikania species, both previously placed in the genus Kanimia, afforded in addition to known compounds several new germ  相似文献   
8.
An investigation of Ursinia saxatilis afforded in addition to known compounds a new eudesmanolide derived from ursialpinolide, a germacranolide rel  相似文献   
9.
Artemisia douglasiana afforded, in addition to known compounds, two new C14-acetylenes, five longipinene derivatives, three nerolidol derivatives, a lactone and a ketone with a new carbon skeleton and lavendulol-2-methylbutyrate. The structures were elucidated by spectroscopic methods and some chemical transformations. The configurations of several oxo longipinene-7, 9-di- and 7, 8, 9-triesters isolated previously were corrected. The biogenesis of the new lactones is discussed briefly.  相似文献   
10.
Abstract. Cell proliferation kinetics of the sarcoma induced by Moloney virus was studied in newborn Swiss OFl mice.
After in vivo injection of tritiated thymidine, followed by autoradiography, it was shown that the majority of cells were actively proliferating (labelling index; 31%, growth fraction 78%). The mean cell cycle was 16 hr and cell loss was relatively low (cell loss factor 48%). The study of tumour specific activity with time after a single [ in vivo ] injection of [3H]dR or [125I]UdR did not demonstrate the same degree of cell loss as that calculated by autoradiography. This result is consistent with a massive reutilization of radioactivity released by normal tissues.  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