全文获取类型
收费全文 | 15549篇 |
免费 | 1492篇 |
国内免费 | 2篇 |
出版年
2023年 | 52篇 |
2022年 | 147篇 |
2021年 | 299篇 |
2020年 | 149篇 |
2019年 | 227篇 |
2018年 | 285篇 |
2017年 | 244篇 |
2016年 | 507篇 |
2015年 | 794篇 |
2014年 | 846篇 |
2013年 | 1020篇 |
2012年 | 1289篇 |
2011年 | 1161篇 |
2010年 | 749篇 |
2009年 | 728篇 |
2008年 | 919篇 |
2007年 | 945篇 |
2006年 | 868篇 |
2005年 | 860篇 |
2004年 | 795篇 |
2003年 | 799篇 |
2002年 | 751篇 |
2001年 | 147篇 |
2000年 | 91篇 |
1999年 | 165篇 |
1998年 | 201篇 |
1997年 | 149篇 |
1996年 | 127篇 |
1995年 | 130篇 |
1994年 | 119篇 |
1993年 | 117篇 |
1992年 | 106篇 |
1991年 | 85篇 |
1990年 | 81篇 |
1989年 | 70篇 |
1988年 | 73篇 |
1987年 | 52篇 |
1986年 | 74篇 |
1985年 | 76篇 |
1984年 | 86篇 |
1983年 | 51篇 |
1982年 | 82篇 |
1981年 | 60篇 |
1980年 | 63篇 |
1979年 | 48篇 |
1978年 | 26篇 |
1977年 | 38篇 |
1976年 | 24篇 |
1974年 | 32篇 |
1970年 | 23篇 |
排序方式: 共有10000条查询结果,搜索用时 312 毫秒
91.
P Raychaudhuri E A Stringer D M Valenzuela U Maitra 《The Journal of biological chemistry》1984,259(19):11930-11935
A ribosomal subunit antiassociation activity has been purified from both the postribosomal supernatant and ribosomal salt-wash protein fractions of rabbit reticulocyte lysates. A majority (greater than 90%) of the activity is associated with a low molecular weight protein of Mr of approximately 25,000. A small but significant level of antiassociation activity (less than 10%) was found to be associated with higher molecular weight protein fractions. The purified 25,000-dalton antiassociation factor interacts with 60 S ribosomal subunits to prevent them from reassociating with 40 S ribosomal subunits. The factor does not seem to interact directly with 40 S subunits nor does it dissociate 80 S monosomes. The properties of this factor are thus similar to the eukaryotic initiation factor 6 isolated from both wheat germ and calf liver extracts. 相似文献
92.
J. S. Julliot Ilona Dusha Marie Hélène Renalier Betty Terzaghi Anne Marie Garnerone P. Boistard 《Molecular & general genetics : MGG》1984,193(1):17-26
Summary We integrated the RP4 plasmid into a selected region of the pSym megaplasmid of Rhizobium meliloti 2011 by homologous recombination between pSym and a cloned fragment of pSym present in the RP4. This cointegrate was used to mobilize into Escherichia coli a Tn5 transposon located on pSym in the vicinity of the site of integration of the RP4. By this technique we obtained a series of RP4-primes that contained large fragments of the pSym megaplasmid and that were most probably generated by IS8 promoted deletions in the RP4-pSym cointegrate. One of them, pGMI42, which carries nitrogenase genes nifD and H as well as nodulation genes, was used for mutagenesis of the corresponding region of pSym after insertion of the Mu prophage into the tet gene. When various (pGMI-42:: Mu)::Tn7 were introduced into R. meliloti 2011 by conjugation, homologous recombination allowed insertion of Tn7 into pSym whereas the pGMI42::Mu was lost due to the suicide effect of Mu. In this way we obtained several symbiotic mutants deficient in either nodulation (Nod-) or nitrogen fixation (Fix-) in association with the host plant Medicago sativa.This paper is affectionately dedicated to the memory of Jean-Simon Julliot who initiated and inspired this work and who was killed by an avalanche on February 21, 1982 相似文献
93.
The effect of ampicillin and tylosin on the faecal enterococci of healthy young chickens 总被引:2,自引:2,他引:0
Enterococcal isolates from young chickens were differentiated into one of three species, namely Enterococcus faecalis, Ent. faecium and Ent. gallinarum . The proportion of each species among the enterococcal population changed with time in birds not dosed with antibiotics. This pattern of change was modified in birds dosed with either tylosin or ampicillin even though ampicillin did not select for ampicillin resistance among the enterococcal population. A gradual increase in tylosin resistance was recorded with time among the enterococci of the 'undosed' control birds. This was associated with an increase in the proportion of Ent. faecium , a species commonly resistant to tylosin, among the enterococci of the birds as they grew older. 相似文献
94.
Several models have been proposed to interpret the mechanism of proton-pumping associated with the electron transfer reactions in the cytochrome b/f complex. Energetics considerations suggest that the proton pump is coupled to the oxidation of cytochrome b by plastoquinone. Experiments performed in living cells under anaerobic conditions suggest that proton-pumping can occur through two independent mechanisms. When the two b cytochromes are reduced prior to a flash illumination i.e. after a long dark anaerobic incubation (>10 minutes), proton-pumping is very likely associated with the reduction of a semiquinone by cyt b which occurs at a site close to the inner face of the membrane. The electrogenic phase is associated with the tranfer of protons via a transmembrane channel. This process is not inhibited by 2-n-nonyl-4-hydroxyquinoline N-oxide (NQNO). Under repetitive-flash or under aerobic conditions, proton-pumping occurs according to a modified Q-cycle mechanism, which is inhibited by NQNO.Dedicated to Prof. L.N.M. Duysens on the occasion of his retirement 相似文献
95.
96.
Dr. Olivier Kah Bernard Breton Joseph G. Dulka Jésus Nunez-Rodriguez Richard E. Peter Anne Corrigan Jean E. Rivier William W. Vale 《Cell and tissue research》1986,244(2):327-337
Summary The organization of Gn-RH systems in the brain of teleosts has been investigated previously by immunohistochemistry using antibodies against the mammalian decapeptide which differs from the teleostean factor. Here, we report the distribution of immunoreactive Gn-RH in the brain of goldfish using antibodies against synthetic teleost peptide.Immunoreactive structures are found along a column extending from the rostral olfactory bulbs to the pituitary stalk. Cell bodies are observed within the olfactory nerves and bulbs, along the ventromedial telencephalon, the ventrolateral preoptic area and the latero-basal hypothalamus. Large perikarya are detected in the dorsal midbrain tegmentum, immediately caudal to the posterior commissure. A prominent pathway was traced from the cells located in the olfactory nerves through the medial olfactory tract and along all the perikarya described above to the pituitary stalk. In the pituitary, projections are restricted to the proximal pars distalis. A second immunoreactive pathway ascends more dorsally in the telencephalon and arches to the periventricular regions of the diencephalon. Part of this pathway forms a periventricular network in the dorsal and posterior hypothalamus, whereas other projections continue caudally to the medulla oblongata and the spinal cord. Lesions of the ventral preoptic area demonstrate that most of the fibers detected in the pituitary originate from the preoptic region. 相似文献
97.
Peter Hersey Anne Edwards Gennaro D'Alessandro Malcolm MacDonald 《Cancer immunology, immunotherapy : CII》1986,22(3):221-231
Summary Patients with stage II melanoma were vaccinated with vaccinia virus-induced melanoma cell lysates (VMCL). The vaccine contained viable vaccinia virus, membranous fragments and no intact nuclei. A number of antigens defined by monoclonal antibodies were detected in the vaccine including the ganglioside GD3 and DR antigens. Administration of the vaccine was associated with depression of natural killer cell activity against melanoma and K562 target cells in the first 3–6 months of treatment. Leucocyte dependent antibody (LDA) activity against melanoma cells was induced or increased in titre in approximately half of the patients studied. Continued vaccination was associated in a number of patients with a decrease in LDA titres. Studies on a small sample of patients revealed that this was associated with the development of serum factors which inhibited LDA activity. LDA activity appeared directed to non-MHC antigens on melanoma cells which were of at least two specificities. One specificity which was shared with antigens on a number of non-melanoma carcinoma cells was removed by absorption on fetal brain and may be similar to oncofetal antigens described by other workers. Reactivity against melanocytes was induced in some patients and may underlie the development of vitiligo in several patients. These results suggest that vaccines prepared from VMCL may be a favourable method for increasing immune responses against melanoma. 相似文献
98.
Diane S. Herson Balkumar Marthi Mary Anne Payer Dr. Katherine H. Baker 《Current microbiology》1986,13(2):77-80
Direct microscopic enumeration ofEnterobacter cloacae with the acridine orange 2-(p-iodophenyl)-3-(p-nitrophenyl)-5-phenyl tetrazolium chloride technique (AOINT) was compared with spread plate counts on nonselective media to establish the usefulness of the former technique in the enumeration of chlorine-stressed cells. Results indicate that the techniques are comparable when the organisms are not stressed. However, AOINT is more sensitive than are plate counts in the detection of chlorine-stressed cells. 相似文献
99.
This study was designed to investigate the mitotic response to wounding in the rat thyroid. The spatial distribution of mitotic activity 48 hr after incision of the thyroid isthmus, or mere exposure of the gland (sham-operation), was assessed using a stathmokinetic technique. Incision resulted in a 66-fold increase over normal in metaphase index adjacent to the wound, falling over 2 mm to a stable 13-fold elevation. Sham-operation produced a smaller response with a complete return to normal levels over 1-1 X 5 mm. The results demonstrate that there is a dramatic localized mitotic response to wounding in the thyroid together with a smaller generalized response. Further, the response to sham-operation indicates that thyroid follicular cells respond to a diffusible 'wound hormone'. We suggest that this may be a major mechanism mediating reparative growth in this gland. 相似文献
100.
The purpose of this study was to investigate the coexistence of gamma-aminobutyric acid (GABA) and leu-enkephalin in single neurons from the corpus striatum. Monolayer cell cultures, started from newborn rat corpus striatum, were grown in serum-free medium and examined using GABA autoradiography and leu-enkephalin immunocytochemistry in a double-label protocol. Examples of cells were found which were positive for one or the other neurotransmitter or for neither transmitter, but not for both. Furthermore, cells which appear similar by morphological criteria alone differed in transmitter specificity. We conclude that the two transmitters tested are not localized within single cells and that morphology alone is inadequate to identify functional cell classes in this area. 相似文献