全文获取类型
收费全文 | 7652篇 |
免费 | 652篇 |
国内免费 | 3篇 |
出版年
2021年 | 87篇 |
2020年 | 69篇 |
2019年 | 66篇 |
2018年 | 113篇 |
2017年 | 90篇 |
2016年 | 143篇 |
2015年 | 264篇 |
2014年 | 308篇 |
2013年 | 354篇 |
2012年 | 517篇 |
2011年 | 466篇 |
2010年 | 314篇 |
2009年 | 267篇 |
2008年 | 417篇 |
2007年 | 435篇 |
2006年 | 412篇 |
2005年 | 402篇 |
2004年 | 376篇 |
2003年 | 383篇 |
2002年 | 362篇 |
2001年 | 146篇 |
2000年 | 110篇 |
1999年 | 117篇 |
1998年 | 128篇 |
1997年 | 78篇 |
1996年 | 72篇 |
1995年 | 100篇 |
1994年 | 86篇 |
1993年 | 85篇 |
1992年 | 89篇 |
1991年 | 68篇 |
1990年 | 72篇 |
1989年 | 53篇 |
1988年 | 66篇 |
1987年 | 56篇 |
1986年 | 56篇 |
1985年 | 63篇 |
1984年 | 66篇 |
1983年 | 61篇 |
1982年 | 59篇 |
1981年 | 51篇 |
1980年 | 54篇 |
1979年 | 53篇 |
1978年 | 49篇 |
1977年 | 46篇 |
1975年 | 41篇 |
1974年 | 49篇 |
1972年 | 38篇 |
1970年 | 42篇 |
1969年 | 54篇 |
排序方式: 共有8307条查询结果,搜索用时 15 毫秒
101.
102.
Imino proton assignments in the proton nuclear magnetic resonance spectrum of the lambda phage OR3 deoxyribonucleic acid fragment 总被引:4,自引:0,他引:4
E L Ulrich E M John G R Gough M J Brunden P T Gilham W M Westler J L Markley 《Biochemistry》1983,22(19):4362-4365
The 17 base pair duplex d(TATCACCGCAAGGGATAp) . d(TATCCCTTGCGGTGATAp) corresponding to the OR3 operator site of lambda phage has been synthesized and studied by 1H nuclear magnetic resonance spectroscopy at 470 MHz. The 13 imino proton resonances observed at 20 degrees C have been assigned to specific base pairs at positions 3-15 on the basis of nuclear Overhauser effect measurements and studies of the temperature dependence of peak intensities. Resonances from the A-T base pairs at positions 1, 2, 16, and 17 are assumed to be absent from the spectrum because of terminal fraying. Resonance from many of the base pairs suggested by Ohlendorf et al. [Ohlendorf, D. H., Anderson, W. F., Fisher, R. G., Takeda, Y., & Matthews, B. W. (1982) Nature (London) 298, 718-723] to be involved in specific binding of the lambda phage cro repressor are well resolved. 相似文献
103.
104.
105.
The urinary excretion of C21- and C19-steroids was investigated in female babons (Papio hamadryas) treated with the ovulation inhibitor Ovosiston (mestranol + chlormadinone-acetate), in comparison with an untreated control Group Urinary C21-steroid excretion was not significantly altered by Ovosiston. 17-Ketosteroids were decreased, predominantly 11-oxygenated compounds. 相似文献
106.
Dr. Christoph Schubert 《Cell and tissue research》1974,156(1):103-112
Summary Dorsal tubercle and skin of Mertensiella caucasica have been investigated with the electron microscope and enzyme histochemical methods. The epidermis of the tubercle consists of 8–9 cell layers, that of normal dorsal skin of 5–6. The tubercle is filled with large mucous glands which are surrounded by an almost complete layer of smooth muscle cells (myoepithelial cells). Their glandular cells undergo cyclical changes and are characterized by specific secretory granules, which differ from those of the relatively small mucous glands of the normal dorsal skin.In the connective tissue of the tubercle a relatively rich supply of nerve fibres has been found, which in part contain synaptic and dense core vesicles or accumulations of mitochondria. In the normal dorsal skin nerve fibres occur less frequently.The following enzymes have been demonstrated in the mucous glands of the tubercle: SDH, acid phosphatase, unspecific esterases, E 600 resistant esterase.The tubercle seems to stimulate the female cloaca chemically and mechanically. 相似文献
107.
Chromosomen-Aktivität und biochemische Zelldifferenzierung in den Speicheldrüsen von Camptochironomus 总被引:3,自引:3,他引:0
Ulrich Grossbach 《Chromosoma》1969,28(2):136-187
Salivary glands of Camptochironomus tentans and C. pallidivittatus were used to study the question whether genes controlling the synthesis of characteristic cell proteins are located in chromomeres specifically puffed in this tissue. Salivary gland cells produce considerable amounts of secretory proteins. In G. tentans, this secretion was shown by gel electrophoresis to consist essentially of 5 protein subunits. In C. pallidivittatus, a component (no. 6) additional to these was found. Another constituent of the secretion (no. 7) is synthesized in C. pallidivittatus by only a small group of gland cells. — The inheritance of these species- and cellspecific proteins has been investigated by relating their presence in interspecific hybrids to the chromosome constitution. Fraction no. 6 was found to be correlated to a short distal region of chromosome IV in which a tissue-specific Balbiani ring is located. Secretion component no. 7 which is characteristic of the special gland lobe of C. pallidivittatus is also controlled by chromosome IV which in this lobe develops a cell-specific Balbiani ring.
Herrn Professor Dr. W. Beermann bin ich für die Anregung zu dieser Arbeit, sein stetes, förderndes Interesse und die Überlassung aller Arbeitsmöglichkeiten zu großem Dank verpflichtet. Ferner möchte ich Herrn E. Freiberg für das verständnisvolle Ausführen der Zeichnungen und Herrn Peinmechanikermeister H. Braun für seine vielfältige Hilfe herzlich danken. 相似文献
Herrn Professor Dr. W. Beermann bin ich für die Anregung zu dieser Arbeit, sein stetes, förderndes Interesse und die Überlassung aller Arbeitsmöglichkeiten zu großem Dank verpflichtet. Ferner möchte ich Herrn E. Freiberg für das verständnisvolle Ausführen der Zeichnungen und Herrn Peinmechanikermeister H. Braun für seine vielfältige Hilfe herzlich danken. 相似文献
108.
109.
Callus from hypocotyl, stem, and fruit tissue of tomato mutants was grown on a complex pea extract medium. The genotypes responded differently to the levels of nutrients and stimulators or inhibitors in the medium. Hypocotyl callus of yellow (r) tomato required K(2) SO(4) for quick establishment and continued steady growth for several months; callus of this mutant could also grow with 0.5 % dimethyl sulfoxide in the medium, although growth was less than the control. The red ghost (r(+) gh) mutant is sensitive to a toxic component in the pea extract, and makes its best growth with the standard minerals and vitamins, but in 1/2 concentration pea extract plus 5 % coconut water. Tangerine (t), red lutescent stem (r(+) l(2) ), and r(+) gh are mutants which respond differently to thiourea: t grows about the same at all concentrations, r(+) gh grows best at low thiourea, and r(+) l(2) grows best at the specific level of 20 mg/l thiourea. The recent active t or r(+) l(1) and r(+) l(2) isolates require supplementary auxin to which the older, slow-growing isolates do not respond. However, there is variation in growth response of different isolates of the same mutant. The several red (r(+) ) cultures are similar in their slow growth, but somewhat different in responses to specific nutrients. The recent (+) isolate is one of the most active cultures, in comparison to the slow growth of t callus isolated in 1964. It is therefore concluded that growth is affected both by the specific requirements of the mutant and by the age and vigor of isolates. 相似文献
110.
Zusammenfassung Das Epithel der Kopfanhänge von elf marinen und Süßwasserprosobranchiern besteht aus prismatischen bis kubischen Stützzellen mit meist dichtem Mikrovillussaum und z.T. Pigmentgranula sowie Sinneszellen, die fast immer in Form sekundärer Sinneszellen vorliegen; nur bei Patella coerulea kommen vermutlich auch primäre Sinneszellen vor. Ihr Zytoplasma ist apikal durch glattwandige E. R.-Zisternen, helle Bläschen und Mikrotubuli gekennzeichnet. Außerdem tragen diese Zellen Zilien und stehen basal mit Nervenendigungen in Kontakt, die sich in drei Gruppen einteilen lassen: 1. Vermutlich cholinerge Endigungen mit optisch leeren Bläschen (Ø 600–800 Å). 2. Endigungen mit dense core vesicles (Ø 1000–1100 Å). Die Annahme, daß diese Endigungen biogene Amine enthalten, wird durch fluoreszenzmikroskopische Befunde gestützt. 3. Endigungen mit großen (Ø 3000–4000 Å) neurosekretorischen Elementargranula.
Structure and innervation of the cephalic tentacles of Prosobranch molluscs
Summary The epithelium of the cephalic tentacles of eleven marine and freshwater prosobranch snails consists of villus bearing supporting cells, which partly contain pigment granules, and sensory cells, which occur in form of secondary sensory cells with the exception of Patella coerulea which presumably possesses primary sensory cells. These receptor cells are characterized as chemoreceptors by apical cilia, smooth surfaced E.R., microtubulues and empty vesicles. At their bases they are in close contact with nerve endings which can be classified in three groups: 1. presumably cholinergic endings with clear vesicles (Ø 600–800 Å). 2. endings with dense core vesicles (Ø 1000–1100 Å). The assumption that these endings contain biogenic amines is supported by positive fluorescence microscopical tests. 3. Endings with big (Ø 3000–4000 Å) neurosecretory elementary granules.
Herrn Prof. Dr. W. Bargmann danke ich für die Überlassung eines Arbeitsplatzes im Anatomischen Institut Kiel. 相似文献