全文获取类型
收费全文 | 4391篇 |
免费 | 407篇 |
专业分类
4798篇 |
出版年
2022年 | 35篇 |
2021年 | 43篇 |
2020年 | 40篇 |
2019年 | 32篇 |
2018年 | 61篇 |
2017年 | 38篇 |
2016年 | 87篇 |
2015年 | 134篇 |
2014年 | 136篇 |
2013年 | 225篇 |
2012年 | 276篇 |
2011年 | 266篇 |
2010年 | 181篇 |
2009年 | 193篇 |
2008年 | 230篇 |
2007年 | 200篇 |
2006年 | 187篇 |
2005年 | 211篇 |
2004年 | 197篇 |
2003年 | 196篇 |
2002年 | 179篇 |
2001年 | 60篇 |
2000年 | 73篇 |
1999年 | 72篇 |
1998年 | 75篇 |
1997年 | 51篇 |
1996年 | 48篇 |
1995年 | 57篇 |
1994年 | 46篇 |
1993年 | 51篇 |
1992年 | 54篇 |
1991年 | 52篇 |
1990年 | 29篇 |
1989年 | 52篇 |
1988年 | 37篇 |
1987年 | 39篇 |
1986年 | 29篇 |
1985年 | 47篇 |
1984年 | 49篇 |
1983年 | 36篇 |
1982年 | 44篇 |
1981年 | 37篇 |
1980年 | 35篇 |
1979年 | 47篇 |
1978年 | 48篇 |
1977年 | 30篇 |
1976年 | 29篇 |
1975年 | 25篇 |
1974年 | 34篇 |
1973年 | 27篇 |
排序方式: 共有4798条查询结果,搜索用时 31 毫秒
101.
Weide B Eigentler TK Pflugfelder A Leiter U Meier F Bauer J Schmidt D Radny P Pföhler C Garbe C 《Cancer immunology, immunotherapy : CII》2011,60(4):487-493
Systemic high-dose interleukin-2 (IL-2) treatment achieves long-term survival in a subset of advanced patients with melanoma.
As we reported previously, intratumoral IL-2 induced complete local responses in more than 60% of melanoma patients. This
study aimed to analyze the long-term outcome of 72 patients treated in two prior trials. Melanoma patients (49 stage III,
23 stage IV) with injectable metastases received intratumoral IL-2 injections thrice weekly at individually escalated doses
(median duration, 6.5 weeks; median total IL-2 dose, 72 MIU; median number of injected metastases, 10). The observed 2-year
overall survival rates were 95.5% for stage III patients with cutaneous metastases only (stage IIIB), 72% for those with combined
cutaneous and lymph node involvement (stage IIIC), 66.7% for stage IV patients with disease limited to distant soft-tissue
metastases (stage IV M1a), and 9.1% for those with visceral metastases (stage IV M1b and stage IV M1c). Thirty patients who
reported recurrence of unresectable distant metastases subsequently received chemotherapy in the further course of disease
and showed an overall response rate of 36.7% (16.7% complete responses, 20% partial responses). A high total dose of IL-2
and a dacarbazine/temozolomide-based chemotherapy regimen were variables correlated with a clinical response. In conclusion,
patients with cutaneous metastasis without lymph node involvement in stage III and with soft-tissue metastasis without visceral
involvement in stage IV showed unexpected favorable survival rates after intratumoral treatment with IL-2. Furthermore, the
intratumoral IL-2 treatment seemed to be associated with increased complete and partial responses in subsequent chemotherapies. 相似文献
102.
The alanine racemase of Mycobacterium smegmatis is essential for growth in the absence of D-alanine 下载免费PDF全文
Alanine racemase, encoded by the gene alr, is an important enzyme in the synthesis of d-alanine for peptidoglycan biosynthesis. Strains of Mycobacterium smegmatis with a deletion mutation of the alr gene were found to require d-alanine for growth in both rich and minimal media. This indicates that alanine racemase is the only source of d-alanine for cell wall biosynthesis in M. smegmatis and confirms alanine racemase as a viable target gene for antimycobacterial drug development. 相似文献
103.
Plant volatiles mediate attraction to host and non-host plant in apple fruit moth, Argyresthia conjugella 总被引:1,自引:0,他引:1
Marie Bengtsson Gunnhild Jaastad Geir Knudsen Sverre Kobro Anna-Carin Bäckman Eva Pettersson & Peter Witzgall 《Entomologia Experimentalis et Applicata》2006,118(1):77-85
Plant volatiles mediate host finding in insect herbivores and lead to host fidelity and habitat‐specific mating, generating premating reproductive isolation and facilitating sympatric divergence. The apple fruit moth, Argyresthia conjugella Zeller (Lepidoptera: Argyresthiidae), is a particularly suitable species to study the cues and behavioural mechanisms leading to colonization of a new host: it recurrently oviposits on the non‐host plant, apple Malus domestica Borkh. (Rosaceae), where the larvae cannot complete their development. The larval host of the apple fruit moth (Lepidoptera, Argyresthiidae), is rowan Sorbus aucuparia L. (Rosaceae). Fruit setting in rowan, however, fluctuates strongly over large areas in Scandinavia. Every 2–4 years, when too few rowanberries are available for egg laying in forests, apple fruit moth females oviposit instead on apple in nearby orchards, but not on other fruits, such as pear or plum. This poses the question of which cues mediate attraction to rowan and apple, and how apple fruit moth discriminates rowan from apple. Chemical analysis and antennal recordings showed that 11 out of 15 rowan volatiles eliciting an antennal response in A. conjugella females co‐occur in rowan and apple headspace, in a different proportion. In the field, A. conjugella was attracted to several of these plant volatiles, especially to 2‐phenyl ethanol, methyl salicylate, and decanal. Addition of anethole to 2‐phenyl ethanol had a strong synergistic effect, the 1 : 1 blend is a powerful attractant for A. conjugella males and females. These results confirm that volatiles common to both plants may account for a host switch in A. conjugella from rowan to apple. Some of the most attractive compounds, including 2‐phenyl ethanol, anethole, and decanal, which have been found in several apple cultivars, were not present in the headspace of the apple cultivar, Aroma, which is also susceptible to attack by A. conjugella. This supports the idea that the odour signal from apple is suboptimal for attraction of A. conjugella, but is nonetheless sufficient for attraction, during times when rowan is not available for egg laying. 相似文献
104.
Jared Cumming Suresh Babu Ying Huang Carolyn Carrol Xia Chen Leonard Favreau William Greenlee Tao Guo Matthew Kennedy Reshma Kuvelkar Thuy Le Guoqing Li Nansie McHugh Peter Orth Lynne Ozgur Eric Parker Kurt Saionz Andrew Stamford Corey Strickland Dawit Tadesse Qi Zhang 《Bioorganic & medicinal chemistry letters》2010,20(9):2837-2842
With collaboration between chemistry, X-ray crystallography, and molecular modeling, we designed and synthesized a series of novel piperazine sulfonamide BACE1 inhibitors. Iterative exploration of the non-prime side and S2′ sub-pocket of the enzyme culminated in identification of an analog that potently lowers peripheral Aβ40 in transgenic mice with a single subcutaneous dose. 相似文献
105.
106.
Ant protection of extrafloral nectar (EFN)-secreting plants is a common form of mutualism found in most habitats around the world. However, very few studies have considered these mutualisms from the ant, rather than the plant, perspective. In particular, a whole-colony perspective that takes into account the spatial structure and nest arrangement of the ant colonies that visit these plants has been lacking, obscuring when and how colony-level foraging decisions might affect tending rates on individual plants. Here, we experimentally demonstrate that recruitment of Crematogaster opuntiae (Buren) ant workers to the EFN-secreting cactus Ferocactus wislizeni (Englem) is not independent between plants up to 5 m apart. Colony territories of C. opuntiae are large, covering areas of up to 5,000 m2, and workers visit between five and 34 EFN-secreting barrel cacti within the territories. These ants are highly polydomous, with up to 20 nest entrances dispersed throughout the territory and interconnected by trail networks. Our study demonstrates that worker recruitment is not independent within large polydomous ant colonies, highlighting the importance of considering colonies rather than individual workers as the relevant study unit within ant/plant protection mutualisms. 相似文献
107.
Kurt W. Schmid Birgit Kunk Rudolf Kirchmair Martin T?tsch Werner B?cker Reiner Fischer-Colbrie 《The Histochemical journal》1995,27(6):473-481
Summary An antiserum raised against a synthetic peptide derived from the primary amino sequence of rat secretogranin II (chromogranin
C) was used for immunological (quantitative radioimmunoassay analysis) and immunohistochemical studies of normal human endocrine
and nervous tissues. This antibody recognized a novel and biologically active neuropeptide which was coined as secretoneurin.
In endocrine tissues, secretoneurin was mainly co-localized with chromogranin A and B with some exceptions (e.g., parathyroid
gland). Secretoneurin was demonstrated immunohistochemically in the adrenal medulla, thyroid C cells, TSH- and FSH/LH-produting
cells of the anterior pituitary, A and B cells of pancreatic islets, in endocrine cells of the gastrointestinal tract and
the bronchial mucosa, and the prostate. Immunoreactivity determined by radioimmunoassay analysis revealed high secretoneurin
levels in the anterior and posterior pituitary and lower levels in pancreatic and thyroid tissue. A strong secretoneurin immunoreactivity
was also found in ganglion cells of the submucdsal and myenteric plexus of the gastrointestinal tract, and in ganglionic cells
of dorsal root ganglia, peripheral nerves, and ganglion cells of the adrenal medulla. Thus, secretoneurin may serve as a useful
marker of gangliocytic/neuronal differentiation. 相似文献
108.
Kurt Haselwandter Gerlinde Häninger Markus Ganzera Hubertus Haas Graeme Nicholson Günther Winkelmann 《Biometals》2013,26(6):969-979
A screening for siderophores produced by the ectomycorrhizal fungi Laccaria laccata and Laccaria bicolor in synthetic low iron medium revealed the release of several different hydroxamate siderophores of which four major siderophores could be identified by high resolution mass spectrometry. While ferricrocin, coprogen and triacetylfusarinine C were assigned as well as other known fungal siderophores, a major peak of the siderophore mixture revealed an average molecular mass of 797 for the iron-loaded compound. High resolution mass spectrometry indicated an absolute mass of m/z = 798.30973 ([M + H]+). With a relative error of Δ = 0.56 ppm this corresponds to linear fusigen (C33H52N6O13Fe; MW = 797.3). The production of large amounts of linear fusigen by these basidiomycetous mycorrhizal fungi may possibly explain the observed suppression of plant pathogenic Fusarium species. For comparative purposes Fusarium roseum was included in this study as a well known producer of cyclic and linear fusigen. 相似文献
109.
Small diameter (<1.0-mm) Acer saccharum Marsh roots were separated into white, brown and woody development state classes and analyzed for total N and C concentrations in April, July and October of 1988. White roots had greater concentrations of N and C than either brown or woody roots at each sampling date, and the N concentration of brown roots was consistently greater than that of woody roots. There were no temporal changes in N concentrations in any of the roots. C was slightly elevated in mid-summer in all three classes of roots. The data suggest the possible existence of an N translocation mechanism in ageing and developing fine roots. More research should be undertaken to establish the mechanisms of N loss in developing fine roots. 相似文献
110.
In the present study the main aim was to investigate the odour mechanisms affecting habitat preferences of Coccinella septempunctata (L.). In a field study, the frequency of adult C. septempunctata was higher in barley plots containing high densities of the common weeds Cirsium arvense (L.) Scop. and Elytrigia repens (L.) Nevski. than in control plots with only barley. In olfactometer experiments in the laboratory, adult C. septempunctata showed a significantly more positive response to mixed odours of barley and each of the two weeds than to barley alone. Ladybirds responded differently to barley plants that were previously exposed to volatiles from the two weeds. The E. repens -exposed barley plant lost its attractivity while the C. arvense -exposed barley plants maintained attractivity. As no aphids or pollen resources were present in the plots during the experiment, the results show that C. septempunctata responds to the botanical characteristics of the habitat even if no food resources are available. These results strongly suggest that olfactory cues and plant-plant communication from diversified plant stands can be important mechanisms in predator attraction to sites with a complex botanical diversity. 相似文献