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   898篇
  免费   62篇
  国内免费   1篇
  2014年   9篇
  2013年   20篇
  2012年   21篇
  2011年   24篇
  2010年   24篇
  2009年   18篇
  2008年   17篇
  2007年   19篇
  2006年   20篇
  2005年   14篇
  2004年   14篇
  2002年   9篇
  1999年   9篇
  1998年   10篇
  1997年   13篇
  1996年   11篇
  1993年   9篇
  1992年   15篇
  1991年   10篇
  1990年   12篇
  1989年   10篇
  1988年   21篇
  1987年   12篇
  1986年   11篇
  1985年   9篇
  1984年   15篇
  1983年   10篇
  1982年   16篇
  1981年   14篇
  1979年   13篇
  1978年   15篇
  1977年   10篇
  1976年   10篇
  1975年   14篇
  1974年   13篇
  1973年   9篇
  1971年   10篇
  1969年   9篇
  1966年   9篇
  1959年   25篇
  1958年   43篇
  1957年   21篇
  1956年   30篇
  1955年   33篇
  1954年   34篇
  1953年   29篇
  1952年   29篇
  1951年   30篇
  1950年   32篇
  1949年   23篇
排序方式: 共有961条查询结果,搜索用时 718 毫秒
51.
Sphagnum mosses are major components of peat bogs but populations of many species are under threat due to habitat fragmentation resulting from the cutting of peat for fuel. We have used an intersimple sequence repeat (ISSR)‐based cloning method to develop nine polymorphic nuclear microsatellites for the peat moss species Sphagnum capillifolium. Between three and seven alleles per locus were detected in a sample of 48 haploid gametophytes and levels of gene diversity ranged from 0.5391 to 0.7960. These represent the first microsatellite markers developed for this important genus and most also exhibited cross‐species amplification across a range of common Sphagnum species.  相似文献   
52.
53.
54.
The fossil salmonid †Eosalmo driftwoodensis was originally described from fragmentary specimens. Study of new material of this fossil species confirms that it is a stem-group salmonine, with a mixture of primitive and derived salmonine features in its skull, but with its postcranial skeleton essentially of modern salmonine construction. Two autapomophies define the genus †Eosalmo: a long anterodorsal process of the subopercle meeting the dorsal edge of the bone at an angle of about 60o, and a thin dermal basihyal plate apparently lacking teeth. Its salmonine relationship is supported by eight derived features: (1) posterior part of frontal widely expanded above autosphenotic, (2) hyomandibular fossa on pterotic long, (3) posterior part of endopterygoid extending posteriorly and broadly overlapped by both metapterygoid and quadrate, (4) premaxillary process of maxilla extending dorsally at an angle larger than 10o, (5) infraorbitals 3 to 5 narrow and covering less than anterior half of hyomandibula, (6) presence of suprapreopercle, (7) anterior end of preopercular canal on horizontal arm distinctiy turning to anteroventral corner of preopercle, (8) first uroneural amplified into large fan-shaped stegural, and (9) scales small, with more fhan two lateral line scales per vertebral centrum. Salmonidae are a monophyletic family defined by at least three synapomorphies: posterior surface of epiotic with sulcus, peg-and-socket connection in caudal skeleton, and tetraploid karyotype. Within the Salmonidae, Thymallinae and Salmoninae form a clade based on features from premaxilla, supramaxilla, anguloarticular, and supraorbital.  相似文献   
55.
56.
57.
58.
The physiologic processes by which tendons of the hand heal after injury differ from one part of the hand to another. Although definitive operation immediately after injury is advisable in many cases to avoid infection, factors other than infection may be more important and dictate delay.While early exercise to mobilize the tendon soon after repair would seem logical, actually the process of healing is such that during the third week the tendon is spontaneously freed from adherence to surrounding tissue. Motion earlier than that causes irritation at the point of suture of the two ends of the tendon and increases scar. After completion of the healing process, motion serves to increase the strength of the new tendon fibrils.  相似文献   
59.
Fifty-six patients with rheumatoid arthritis were treated continuously with cortisone for periods ranging between 4 and 38 months, in daily doses of 15 to 100 mg. Concomitant therapy included periods of rest, physical therapy, and salicylates. The incidence of subjective improvement exceeded that of objective improvement. The incidence of objective improvement was higher in females; also, in those patients whose disease was in an early stage and of short duration at the time therapy was begun, and who required relatively smaller maintenance doses of cortisone. Therapeutic results were not affected by the age of the patient or by the presence of spondylitis. Despite precautions, the long-term administration of cortisone was, in some patients, productive of serious undesirable side-effects. Although cortisone usually suppressed the symptoms and signs of rheumatoid arthritis, progression of the disease was frequently noted during its long-term administration.  相似文献   
60.
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