全文获取类型
收费全文 | 44961篇 |
免费 | 3700篇 |
国内免费 | 5篇 |
出版年
2023年 | 223篇 |
2021年 | 349篇 |
2020年 | 296篇 |
2019年 | 294篇 |
2018年 | 908篇 |
2017年 | 929篇 |
2016年 | 996篇 |
2015年 | 859篇 |
2014年 | 1009篇 |
2013年 | 1827篇 |
2012年 | 3134篇 |
2011年 | 3487篇 |
2010年 | 1771篇 |
2009年 | 1146篇 |
2008年 | 2875篇 |
2007年 | 2936篇 |
2006年 | 2734篇 |
2005年 | 2428篇 |
2004年 | 2333篇 |
2003年 | 2186篇 |
2002年 | 2183篇 |
2001年 | 1489篇 |
2000年 | 1741篇 |
1999年 | 906篇 |
1998年 | 437篇 |
1997年 | 346篇 |
1996年 | 419篇 |
1995年 | 352篇 |
1994年 | 379篇 |
1993年 | 341篇 |
1992年 | 356篇 |
1991年 | 294篇 |
1990年 | 269篇 |
1989年 | 249篇 |
1988年 | 238篇 |
1987年 | 245篇 |
1986年 | 207篇 |
1985年 | 297篇 |
1984年 | 362篇 |
1983年 | 326篇 |
1982年 | 304篇 |
1981年 | 292篇 |
1980年 | 258篇 |
1979年 | 252篇 |
1978年 | 261篇 |
1977年 | 239篇 |
1976年 | 240篇 |
1975年 | 284篇 |
1974年 | 208篇 |
1973年 | 197篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
961.
D. Sömjen G.J. Sömjen A. Harell G.L. Mechanic I. Binderman 《Biochemical and biophysical research communications》1982,106(2):644-651
Cytosol preparations and cells from 6-day old cultured differentiating chick limb-bud mesenchyme, which consist of a high proportion of chondrocytes, were shown to specifically bind 24R,25 dihydroxycholecalciferol. Nuclei from identical cultures also showed specific binding for 24R,25 dihydroxycholecalciferol. On the contrary, similar preparations of limb-bud mesenchyme cells (6-day old cultures) pretreated on day one by 5-bromodesoxyuridine which induced a fibroblast phenotypic expression, failed to show any specific binding for either 24R,25 or 1α,25 dihydroxycholecalciferol. Pronase treatment of the cytosol indicated that the receptor was protein-like in nature. The chromatographic properties of the protein-receptor on diethylaminoethyl cellulose and Sephadex G-100 columns were similar to those of the protein receptor found for 1α,25 dihydroxycholecalciferol. This report is the first demonstration that a cytosol protein receptor for 24R,25 dihydroxycholecalciferol exists in developing skeletal tissue. 24,25 dihydroxyvitamin D3 but not any of the other metabolites was shown to induce DNA synthesis after 24 h by almost two-fold and protein synthesis after 5 h by 240%. These results suggest an important physiological role for 24R,25 dihydroxyvitamin D3 in the development of skeletal tissue. 相似文献
962.
Dieter Kabelitz Thomas H. Tötterman Magnus Gidlund Kenneth Nilsson Hans Wigzell 《Cellular immunology》1982,70(2):277-286
Stimulatory effects of the tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA) on human T lymphocytes have been investigated. TPA was found to stimulate highly purified T cells (obtained by a three-step isolation procedure involving plastic adherence, nylon wool passage and Ig-anti-Ig column passage) in the absence of accessory cells (stimulation index of 5 to 10), whereas phytohemaglutinin (PHA) and concanavalin A (Con A) did not. This response was, however, increased by the addition of autologous adherent cells. Addition of TPA, but not adherent cells, induced T-cell proliferation in response to the nonmitogenic lectin, wheat germ agglutinin (WGA), while both adherent cells and TPA restored T-cell proliferation to mitogenic lectins such as PHA and Con A. Furthermore, TPA greatly increased the mixed-lymphocyte response of purified T cells to otherwise nonstimulating allogeneic cells such as T lymphocytes or tumor cells from some patients with chronic lymphocytic leukemia. These results suggest that TPA can directly act on human T cells to render them reactive to a variety of stimuli. 相似文献
963.
Induction and repair of DNA strand breaks in cultured human fibroblasts exposed to various phenols and dihydrodiols of benzo[a]pyrene 总被引:1,自引:0,他引:1
Cultured human fibroblasts from healthy donors were incubated for 30 min with nine different benzo[a]pyrene (BP) derivatives in the presence or absence of liver microsomes from 3-methylcholanthrene treated rats. The induction and repair of DNA strand breaks were analysed by alkaline unwinding and separation of double and single stranded DNA (SS-DNA) by hydroxylapatite chromatography immediately after the incubation or at various times after the treatment. In the absence of microsomes DNA stand breaks were detected in fibroblasts exposed to 30 microM of each of the six BP phenols (1-, 2-, 3-, 7-, 9- or 11-OH-BP) and the three BP dihydrodiols (BP-4,5-, BP-7,8- or BP-9,10-dihydrodiol). After removal of the BP derivatives from the medium the DNA strand breaks disappeared within 24 h. alpha-Naphthoflavone (alpha-NF) caused a decrease in the induction of strand breaks by 1-, 3- and 9-OH-BP but did not affect the induction of strand breaks in cells exposed to BP-7,8-dihydrodiol. In the presence of microsomes DNA strand breaks were found after exposure to 30 microM of each of the six BP phenols (1-, 2-, 3-, 7-, 9- or 11-OH-BP), as well as BP-7,8- and 9,10-dihydrodiol. In contrast BP-4,5-dihydrodiol did not induce strand breaks under these conditions. The induction of strand breaks by BP-7,8-dihydrodiol was enhanced in the presence of cytosine-1-beta-D-arabinofuranoside (AraC). In all cases the DNA strand breaks had disappeared 24 h after removal of the BP derivatives and microsomes except after treatment with BP-7,8-dihydrodiol. 相似文献
964.
965.
Monoclonal antibodies directed against nonhistone chromosomal proteins of D. melanogaster were tested for crossreactivity with the homologous antigens of various Drosophila species. — By indirect immunofluorescence it could be shown that three antibodies react only with polytene chromosomes of species of the D. melanogaster subgroup, and only much less with chromosomes of other species of Drosophila. — With chromosomes of various other species of the Sophophora or Drosophila radiations only a reaction at background level could be observed. — The results suggest that the three antibodies react with different antigenic determinants of a single protein whose conformation changed rather fast during evolution of the Drosophilidae. 相似文献
966.
Géza Fejes-Tóth Anikó Náray-Fejes-Tóth Bart Rigter Jürgen C. Frölich 《Prostaglandins & other lipid mediators》1983,25(1):99-103
To study the relationship between urine flow, urinary prostaglandin (PG) and kallikrein excretion in the rat high urine flow was induced in hydropenic Long-Evans rats by either hypotonic volume expansion or with manniitol or with furosemide. PGE, excretion remained unchanged during hypotonic volume expansion (134.5 ± 29.7 before and 153.0 ± 48.9 pg/min after) while it decreased significantly with mannitol (from 166.3 ± 32.4 to 45.2 ± 8.2 pg/min, p<0.01) and with furosemide (from 170.0 ± 20.4 to 29.5 ± 5.3 pg/min, p<0.001). PGF2α excretion rates were slightly reduced following all three interventions. Urinary kallikrein excretion remained unchanged in all three groups of animals. It is concluded that, in contrast to human and dogs in the rat urine flow and urinary PG excretion are not interlinked. 相似文献
967.
Jaana Rehnström Mutsuo Ishikawa Fritz Fuchs Anna-Riitta Fuchs 《Prostaglandins & other lipid mediators》1983,26(6):973-981
The effect of amniotic fluid obtained from second trimester (16–20 wks) and term pregnancies (38–41 wks) on the production of PGE and F by human amnion, decidua and myometrium at term was determined using tissue slices incubated in vitro. Midpregnancy amniotic fluid neither inhibited nor stimulated the prostanoid production by any of the tissues. In contrast, term amniotic fluid obtained before as well as after the onset of labor markedly increased the production of both PGE and PGF in decidua and myometrium from levels in Krebs solution. The prostanoid production (PGE + PGF) in amnoin was not significantly increased but the proportion of PGF was raised during incubations in term amniotic fluid. In decidua and myometrium the increase in PGE and PGF production in term amniotic fluid was approximately 200 and 400 percent respectively, from control values in Krebs solution. We propose that the stimulatory activity in term amniotic fluid in responsible for the accelerated synthesis of prostaglandins after of membranes, which is reflected in raised PGF metabolite levels in maternal circulation. It may also be the reason for the rise in amniotic fluid prostaglandin levels around the 35th week of gestation, and perhaps for the onset of labor. 相似文献
968.
The macrobenthic fauna associated withFucus at a station in the Kiel Fjord was investigated from June 1978 until June 1979. The predominant group in number as well as in biomass were gammarids. They formed, together with the isopodsIdotea spp., approximately 95 % of the total average annual biomass. The total dry weight of all macrobenthic animals (excl.Littorina spp.) increased from 1.9 g per kgFucus in May to about 16 g in June–August, and dropped to 8.3 g in September. Winter average dry weight values were only about 6 % of the summer values. 相似文献
969.
J. Beitz M. Panse S. Fischer C. Hora W. Förster 《Prostaglandins & other lipid mediators》1983,26(6):885-892
A hypothesis of Gryglewski et al. explains the correlation between increased level of LDL and development of atherosclerosis by inhibition of PGI2 synthesis by increased peroxide content of LDL. The aim of the present paper was to examine this hypothesis. The major results are: 1) Preparation of LDL in the presence of .02 % butylated hydroxytoluene did not reduce the lipid peroxide content of LDL from men and women and not change the inhibition or stimulation of the in vitro biosynthesis of PGI2 by LDL isolated from blood of men or women, respectively. 2) In the LDL and HDL, respectively, of healthy men we found nearly the same lipid peroxide levels (nmole malondialdehyde (MDA)/mg lipoprotein-cholesterol) as in the lipoproteins of male patients with hyperlipidemia type IIa or IV, but the peroxide concentration is three times higher in HDL as in LDL. 3) LDL isolated from healthy men inhibited in dose dependent fashion the generation of PGI2 from PGH2 by aortic microsomes whereas LDL from premopausal women stimulated PGI2 formation even calculated as LDL lipid peroxides (in nM MDA/ml). The results call into question the hypothesis that diminished PGI2 formation by atherosclerotic vessels is related to inhibition of PGI2 synthetase by lipid peroxides present in LDL in the lesions. A new working hypothesis is presented that also the fatty acid pattern and the lipid class composition in the LDL are important for their influence on the PGI2 formation. 相似文献
970.
Hans Lindblom U.-B. Axiö-Rredriksson Edward H. Cooper Ron Turner 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》1983,273(1):107-116
Proteins excreted in urine due to renal failure were separated on Mono QTM, a new strong anion exchanger designed for fast high-resolution protein separations. The separation procedure was divided into two steps. The first step involved removal of low-molecular- weight substances by rapid desalting on a Sephadex G-25 Superfine column. In the second step, the total protein fraction (3–6 ml) was loaded onto the Mono Q column with the aid of a superloop. The proteins were adsorbed onto the top of the ion-exchanger column and gradually displaced by a combined pH and salt gradient in 40 min. The choice of ion exchanger and initial operating conditions were based on data obtained from electrophoretic titration curve experiments. Identification of separated proteins was achieved by fused rocket electrophoresis and sodium dodecyl sulphate-polyacrylamide gel electrophoresis, respectively. 相似文献