全文获取类型
收费全文 | 14186篇 |
免费 | 1109篇 |
出版年
2022年 | 101篇 |
2021年 | 176篇 |
2020年 | 122篇 |
2019年 | 156篇 |
2018年 | 222篇 |
2017年 | 166篇 |
2016年 | 337篇 |
2015年 | 557篇 |
2014年 | 553篇 |
2013年 | 816篇 |
2012年 | 991篇 |
2011年 | 947篇 |
2010年 | 664篇 |
2009年 | 521篇 |
2008年 | 782篇 |
2007年 | 854篇 |
2006年 | 850篇 |
2005年 | 820篇 |
2004年 | 798篇 |
2003年 | 732篇 |
2002年 | 744篇 |
2001年 | 163篇 |
2000年 | 113篇 |
1999年 | 163篇 |
1998年 | 217篇 |
1997年 | 151篇 |
1996年 | 131篇 |
1995年 | 140篇 |
1994年 | 122篇 |
1993年 | 119篇 |
1992年 | 138篇 |
1991年 | 96篇 |
1990年 | 79篇 |
1989年 | 98篇 |
1988年 | 88篇 |
1987年 | 79篇 |
1986年 | 83篇 |
1985年 | 96篇 |
1984年 | 128篇 |
1983年 | 102篇 |
1982年 | 113篇 |
1981年 | 109篇 |
1980年 | 98篇 |
1979年 | 65篇 |
1978年 | 68篇 |
1977年 | 62篇 |
1976年 | 58篇 |
1975年 | 50篇 |
1974年 | 57篇 |
1972年 | 43篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Brunella Franco Li-Wen Lai David Patterson David H. Ledbetter Barbara J. Trask Ger van den Engh Susan Iannaccone Shannon Frances Pragna I. Patel James R. Lupski 《Human genetics》1991,87(3):269-277
Summary We report a patient (S.T.) with multiple congenital anomalies and developmental delay associated with an interstitial deletion of 1q23–1q25. Molecular analysis of the deletion was performed using DNA markers that map to 1q. Five DNA markers, MLAJ-1 (D1S61), CRI-L1054 (D1S42), HBI40 (D1S66), OS-6 (D1S75), and BH516 (D1S110), were demonstrated to be deleted. Informative polymorphisms demonstrated this to be a de novo deletion of the maternally derived chromosome. Deletion status was determined using restriction fragment length polymorphism (RFLP) analysis supplemented with densitometry in the experiments where RFLP analysis was not fully informative. Deletions were confirmed by Southern analysis using genomic DNA from a somatic cell hybrid retaining the del(1)(q23–q25) chromosome that was constructed from patient S.T. Flow karyotyping confirmed the deletion and estimated that the deletion encompassed 11,000–16,000 kb. The clinical and cytogenetic characteristics of S.T. are compared with those of ten previously described patients with monosomy 1q21–1q25. 相似文献
72.
Toshiyuki Itaya Eric Fearon Troy Fiesinger Barbara Hunt Bert Vogelstein Philip Frost 《Cancer immunology, immunotherapy : CII》1991,33(4):267-273
Summary The transfection of murine SP1 tumor cells with the hemagglutinin (HA) gene of influenza virus results, after fluorescent-activated cell sorting (FACS), in the selection of high-HA-expressing cell lines called H4A and H4B. Both lines fail to grow in syngeneic animals at doses that result in 100% tumor take of non-transfected tumor cells. Both grow in immunosuppressed mice. SP1 and H4A or H4B cells express few class I major histocompatibility complex (MHC) antigens but do express class II IAk antigens. H4A or H4B cells engender a cytotoxic T lymphocyte (CTL) response but cannot protect against a challenge with SP1 cells. This CTL response is inhibited by anti-CD4 but not anti-CD8 antibodies. Using FACS, we were able to select a population (called H5AK5) with high class-I MHC antigen expression. Like H4A and H4B, H5AK5 cells fail to grow in syngeneic animals but do grow in immunosuppressed mice. However, unlike H4A or H4B, H5AK5 can induce protection against a challenge with 1 × 105 SP1 cells. These studies indicate that the immunogenicity ofHA-transfected SP1 cells may correlate with the cell-surface expression of class II MHC antigens. However, HA-expressing SP1 cells seem able to induce a protective response against a parent SP1 cell challenge only if they also express class I MHC antigens. This view is supported by the observations that SP1 cells expressing murine interleukin-2 do not express class I MHC antigens, fail to grow in syngeneic animals, do grow in immunosuppressed mice but do not protect against a challenge with parental SP1 cells.This work was supported by The Clayton Fund, The Sid W. Richardson Foundation and PHS grants CA 39853 and 41525. Toshiyuki Itaya is a visiting scientist supported by the Smith Education Fund of the Department of Cell Biology. Troy Fiesinger is a summer research investigator sponsored by The University of Texas M. D. Anderson Cancer Center Summer Program for College Students 相似文献
73.
Seeds of theHordeum patagonicum complex were collected from the field and grown in the greenhouse. The aim was to take a sample of members of the complex, and on the basis of the phenotypic similarities in some morphological and physiological characters, determine whether distinct groups exist. When cluster analyses, to generate hypotheses, and orthodox statistical procedures, for hypotheses obtained a priori, were applied to the reproductive morphology, germination and flowering patterns, onlyH. patagonicum subsp.magellanicum, out of the five recognized taxa, could be distinguished consistently. The remaining four taxa, which overlapped considerably, could be re-formed into three groups whose centroids were different but whose ranges of variation were not distinct from each other. We conclude that the highly cross-compatible members of theH. patagonicum complex, first defined as species and later redefined as subspecies are probably no more than biotypes. 相似文献
74.
Barbara Hickel 《Hydrobiologia》1988,161(1):49-54
A new species of freshwater dinoflagellates, Ceratium rhomvoides nov. sp., is described from the Plußsee, northern West Germany, where it occurs regularly. C. rhomvoides nov. sp. is distinguished from closely related taxa by various aspects of the morphology of the vegetative cell and the cyst and by its sexual reproduction and seasonal distribution. 相似文献
75.
Barbara Hickel 《Hydrobiologia》1988,161(1):41-48
The life cycle of Ceratium furcoides (Levander) Langhans which features sexual reproduction is described for the first time in situ from the lake Plußsee (northern West Germany). Anisogamic copulation occurs during the bloom period in July–August by incorporation of the male gamete by the female gamete, resulting in an overwintering planozygote. The planozygote develops into a benthic hypnozygote which germinates in spring to establish a planomeiocyte. The morphology and structure of the stages of the life cycle are described using light and scanning electron microscopy. 相似文献
76.
Absence of Transient Elevated UV Resistance during Germination of Bacillus subtilis Spores Lacking Small, Acid-Soluble Spore Proteins α and β
下载免费PDF全文
![点击此处可从《Journal of bacteriology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Germinating spores of Bacillus subtilis mutants which lack small, acid-soluble spore proteins α and β did not exhibit the transient elevated UV resistance seen during germination of wild-type spores. 相似文献
77.
Seasonal variations in levels of serum testosterone, dihydrotestosterone (DHT), reproductive behavior, and social behavior were investigated in 12 adult males (5 to 20 + years of age) of the Oregon troop of Japanese macaques (Macaca fuscata). Blood samples were collected at 2- to 4-month intervals, and behaviors were monitored twice weekly over a 15-month period. Significant seasonal variations in levels of testosterone and DHT, and in frequencies of mount series, ejaculations, number of female partners, displays, courtship, and aggression were observed. Seasonal variations in reproductive and social behaviors did not correlate with seasonal variations in androgen levels because seasonal increases in these behaviors followed seasonal increases in the androgens with a 1- to 2-month delay. However, significant correlations between increased androgen levels and the onset of mating activity occur when mean monthly frequencies of mount series are shifted 1 to 2 months earlier to coincide with the rise in serum androgen levels. The frequency of adult male play and male-male mounting increased significantly when androgen levels were low. We suggest that photoperiod changes may function as a proximate cue in male Japanese macaques which induces a state of biological readiness for mating, and the behavioral consequences (i.e., mating) are then dependent upon the presence of receptive females. 相似文献
78.
The binding of germanium to Pseudomonas putida ATCC 33015 was investigated by using whole intact cells grown in a medium supplemented with GeO2 and catechol or acetate. Electron-microscopic examination of the control and metal-loaded samples revealed that germanium was bound within the cell envelope. A certain number of small electron-dense deposits of the bound element were found in the cytoplasm when the cells were grown in the presence of GeO2 and catechol. The study of germanium distribution in cellular fractions revealed that catechol facilitated the intracellular accumulation of this element. 相似文献
79.
Barbara Kluve-Beckerman George L. Long Merrill D. Benson 《Biochemical genetics》1986,24(11-12):795-803
Serum amyloid A (SAA) is an acute-phase reactant and precursor to amyloid A protein, the major constituent of the fibril deposits of reactive amyloidosis. The factors determining whether the 104-amino acid SAA molecule is converted into the 76-amino acid amyloid A protein and deposited as fibrils are not known. As an initial step toward investigating the possibility that a particular primary structure of SAA is involved in amyloid formation, we have cloned and determined the nucleotide sequence of human SAA-specific cDNAs. The first clone, selected using an oligonucleotide probe, was shown to encode the signal peptide and amino-terminal region of SAA. The cDNA of this clone served as probe in the selection of two distinct, full-length SAA cDNAs, initially differentiated by the presence (pSAA21) or absence (pSAA82) of a PstI site in the coding sequence. The complete nucleotide sequence of pSAA82 cDNA was determined. Since there appear to be multiple human SAA alleles, it is conceivable that their differential expression is important to amyloid formation. 相似文献
80.
James V. Moroney N. E. Tolbert Barbara B. Sears 《Molecular & general genetics : MGG》1986,204(2):199-203
Summary Six independently isolated mutants of Chlamydomonas reinhardtii that require elevated CO2 for photoautotrophic growth were tested by complementation analysis. These mutants are likely to be defective in some aspect of the algal concentrating mechanism for inorganic carbon as they exhibit CO2 fixation and inorganic carbon accumulation properties different from the wild-type. Four of the six mutants defined a single complementation group and appear to be defective in an intracellular carbonic anhydrase. The other two mutations represent two additional complementation groups.Abbreviations HS
high salt medium which has 13 mM phosphate at pH 6.8
- HSA
high salt plus 36 mM acetate medium
- YA
high salt medium with 4 g yeast extract per L and 36mM acetate
- Arg
arginine
- cia-
CO2 accumulation mutants that cannot grow on low CO2
- Ci
inorganic carbon (CO2+HCO
-
3
)
- CA
carbonic anhydrase
- mt
mating type
Supported in part by the McKnight Foundation and by NSF grant PCM 8005917 and published as journal article 11924 from the Michigan State Agriculatural Experiment Station 相似文献